Author Topic: Carb recommendations  (Read 26135 times)

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #60 on: March 26, 2018, 07:02:43 PM »


Apex 7 flat works well inserted into a reversible screw driver.
The 3/8 is just big enough.

Lightly hold one finger on the needle and another on the hinge pin, use the other hand to measure at the toe of the float.

If you have an extra spring from the filter you can cut in half, place under the float while holding the hinge pin then measure.

Holding upside down is another way letting the weight of the float do the work while holding the hinge pin.

Don’t forget to put the metal ring back in under the seat and make sure only 1.

Blazer, did you mean put back the rubber ring under the seat?  Your photo appears to show a rubber gasket, and my carb appears to have a rubber gasket.

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #61 on: March 26, 2018, 07:11:59 PM »
Hi Monkey Uncle:
Setting the float height is easier with that paper scale that comes with the rebuild kit...the scale has a white background and the graduations are in black...the paper scale is also a T-square and sized so it can fit in the float chamber and register on the top of the float chamber edge to make the measurement easier and more accurate. I can send you a image of where the measurement is supposed to be on the float arm.

Aneroid insert (stuffer): It appears to me the aneroid cavity has an open slot to the float bowl chamber so it would affect the volume of gas in the float bowl...my gut feel is that the insert should be there otherwise there will be excessive sloshing of gas and hence excessive movement of the float...maybe someone else on the forum can comment on this or maybe Stewart Griffin can open his M4ME carb up and see if there is a aneroid insert in it.

Regards,
Henry

Thanks, Henry.  I'll ask about the aneroid cavity insert when I call to order parts.

Henry and I have been discussing a few other small parts, and I'm wondering if anyone else can shed light on whether my carb is supposed to have them.

Retainer and seal on the top of the accelerator pump stem: These parts appear on an exploded diagram of a M4ME in the book by Doug Roe.  My current pump does not have them, and when I look up the replacement pump for my carb model on quadrajetparts.com, it also does not have these parts.  Also we know from some of the other parts we've discussed that the Roe's exploded diagram does not match my carb in some respects.

Small copper spring on top of the check ball: When I took the check ball retainer screw off, there was a tiny copper spring sitting on top of the check ball.  This seems to be unusual for a Qjet.  Is the spring supposed to be there?

Thanks, guys.

Offline blazer74

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Re: Carb recommendations
« Reply #62 on: March 26, 2018, 07:22:41 PM »
Well the seal in my pic  is metal, it works like a crush washer. That’s what comes with a quality n/s.
I have never seen  a rubber one.
IDK, something the remanufacturer who did your carb used.

If either your n/s or that seal under the seat leaks it will render your float useless and overfill the bowl from the pressure of the pump.

Did you have hot start problems prior to removal of the carb.
As in having to hold the pedal to the floor to get a start after sitting say 15 minutes hot.?


Offline blazer74

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Re: Carb recommendations
« Reply #63 on: March 26, 2018, 08:57:46 PM »
Looked around and the only rubber seal I see is when the threads are stripped and a press in type is used.

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #64 on: March 27, 2018, 05:48:08 AM »
I'll have to look at the ring again - I haven't actually pulled it out and handled it.  It looks like black rubber, so I just assumed that's what it is.  I'll have to double-check the threads also.  The seat backed out normally and did not give me the impression that anything was stripped.

I have not had any major hot start problems since I switched to E0 gas.  Occasionally in hot weather it was a little temperamental on hot re-starts, but I think that was prior to the carb being rebuilt.  Before I switched to E0 gas, hot starts were quite difficult.

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #65 on: March 27, 2018, 12:35:40 PM »
I'll have to look at the ring again - I haven't actually pulled it out and handled it.  It looks like black rubber, so I just assumed that's what it is.  I'll have to double-check the threads also.  The seat backed out normally and did not give me the impression that anything was stripped.

The ring is metal and the threads are not stripped.  Sorry for the confusion.

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #66 on: March 28, 2018, 01:49:53 PM »
Retainer and seal on the top of the accelerator pump stem: These parts appear on an exploded diagram of a M4ME in the book by Doug Roe.  My current pump does not have them, and when I look up the replacement pump for my carb model on quadrajetparts.com, it also does not have these parts.  Also we know from some of the other parts we've discussed that the Roe's exploded diagram does not match my carb in some respects.

I wasn't looking in the right place for the retainer and seal.  They are pressed into the air horn (see photo).

But I'm still wondering about the aneroid insert and check ball spring.

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #67 on: April 11, 2018, 11:07:08 AM »
I rebuilt the carb, but I'm still having some issues.  I did the rebuild kit from Quadrajetparts.com, which included new needle/seat, accel pump cup, check ball, and pump stem seal.  I also did the following:

New nitrophyll float
New power piston retaining ring
New fuel filter and fuel nut gasket
Re-sealed all well plugs with JB Weld Marine grade epoxy (supposed to be resistant to fuel, heat, and expansion/contraction)
Added an aneroid insert that is an exact fit for the cavity
Added the proper link between the vacuum break and the secondary air flap
Removed the spring that was in the check ball well
Ran through the various choke adjustments on the kit's instruction sheet

It appears that the bowl is still over-filling, as evidenced by a saturated air horn gasket and the top of the fuel level being visible through the rear vent.

I went through the standard lean-drop tuning procedure, which seemed to behave normally, but the exhaust still smells rich.  No smoke or soot, though.

Cold starts are difficult; I have to crank for a while and pump accelerator to get it to fire.  No problem with warm/hot re-starts.

The curb idle is relatively normal once it's off of high idle, but after driving for a few minutes, the curb idle speed increases on its own, such that it sounds and feels like high idle.  I verified that the high idle cam is in the lowest position, and also verified that the throttle is not sticking part way open (idle speed adjustment screw is in contact with the throttle stop).

The choke and high idle appear to be working as they should.  Choke snaps shut when the throttle is opened and high idle cam goes up to the high step.  Choke opens a crack once the engine starts, and then gradually opens all the way over the next minute or two.  High idle disengages with a light tap of the pedal.

I'm beginning to think that excessive fuel pressure is the culprit, as I am pretty sure that I got everything reassembled right and the float adjusted right.  I'm considering adjusting the float downward a few 32nds below the spec, just to see if that will generate enough additional buoyant force to close the needle.  Any thoughts on that?

I don't have a gauge with which to check fuel pressure.  The pump looks like the standard stock GM mechanical pump, although I am fairly certain it is not the original pump.  Anyone ever hear of these pumps generating too much pressure.

Thanks.

Offline blazer74

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Re: Carb recommendations
« Reply #68 on: April 11, 2018, 07:35:19 PM »
Many aftermarket pumps put out too much pressure.
Inline gauges are relatively cheap, local parts stores should have one but you will need a section of rubber fuel line to place it in if you still have the all metal fuel line to the carb.

Any more than 7 psi can start causing problems.

You mentioned no hot restart problems which leads away from high fuel pressure though.

You have no way of knowing how the carb is calibrated unless you measure all the passages, jets, rods etc.

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #69 on: April 21, 2018, 07:51:42 AM »
Thanks, Blazer.

After much observation, I am pretty sure that I have two problems with the carb.  First, the bowl is leaking, which is the cause of my cold start problems.  Engine will start after it sits for up to 24 hours, but any longer than that and I have to crank 10-15 seconds to fill the bowl, then it will start normally.  I measured the float level through the vent and confirmed that the float level is low (about 27/32 below top of bowl) when I am having the cold start problem.  I also checked about an hour after running, and there was raw fuel on the floor of the manifold and fuel vapors rose up through the carb when I opened the throttle plate.  It also acts slightly flooded when I wait about an hour before attempting a hot re-start.  So I'm guessing I did something wrong when sealing the well plugs.

Second carb problem is the flooding.  When it is running at idle, I can measure the float level through the vent, and it is at the fully up position (about 3/8 to 13/32).  I can see fuel on top of the float, and at one point I measured the depth of the excess fuel at about 3/8" above the float, which would put the fuel level about even with the top of the bowl.  I guess fuel pressure is the prime suspect at this point, but I'll have to tear the carb down again to make sure something isn't wrong with the installation of the float, needle, and seat.

I think I have discovered a third problem with the distributor, although I'm scratching my head over this one.  With the vacuum advance disconnected and the hose to the carb plugged, I set the initial timing advance at 12* before TDC and the idle to about 830 - 850 rpm (it felt too rough at the factory spec of 700).  When I connected the vacuum advance, the idle increased to approx. 1180 rpm, and the timing displayed 4* after TDC.  The increase in rpm is to be expected when applying the vacuum advance, but the retarded timing seems completely off the wall.  Searching the www, I found one thread on a corvette forum where a guy had a similar problem with vacuum advance appearing to retard the timing.  The solution that was suggested is that somehow the pickup coil wires got reversed and were causing a problem with the firing order when the vacuum advance was applied.  I don't know how that would happen unless it was just a manufacturer's defect in the pickup coil.  Here's the thread - post #28 on page two presents the theory about the pickup coil wires: https://www.corvetteforum.com/forums/c3-tech-performance/2493663-vacuum-advance-is-retarding-my-timing.html

Any thoughts on what might be going on with my distributor?  I should note that when the mechanic replaced the valve train parts recently, the distributor was taken out and the cap was off.  Is there anything he could have done when re-installing it that would cause this problem?

Thanks.

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #70 on: April 21, 2018, 11:24:48 AM »
Here are some pics of the distributor.  Sorry for the poor quality - back of the engine compartment is a tough place to take a picture.

I traced all the spark plug wires and verified that they are all going to the right plug.
« Last Edit: April 21, 2018, 11:27:29 AM by Monkey Uncle »

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #71 on: April 22, 2018, 11:17:03 AM »
Here are some better pics with the rotor off.

I noticed that the mechanic's helpers had not put the distributor cap back on quite right.  The little tab in the back that makes it sit in exactly the right spot was not engaged properly, and one of the hold down clamps was not fastened.  I put the cap back on ensuring that I got all that right, but it had no appreciable effect on the timing anomaly.  It's now reading 10* before TDC without the vacuum advance and 3* after TDC with the vacuum advance hooked up.

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #72 on: April 22, 2018, 01:00:50 PM »
I think I figured out the timing anomaly, and I think it is due to timing light operator error.  It appears that the timing light's pickup is catching the spark from both the number 1 wire and the immediately adjacent number 3 wire.  With the vacuum advance connected and the timing light's advance feature set to 0, the timing mark is advanced out of view when the light flashes from the number 1 wire, while the flash from the number 3 wire happens to be catching the timing mark as it passes the 3* retarded point on the scale.  Increasing the timing light's advance setting to 33 brings the timing mark back to the zero point on the scale.

So it appears that the vacuum advance is adding about 23 degrees of advance at idle.  So now I need to figure out if that is an appropriate amount of advance to be adding at idle.

Sorry for all my confusion.

Edit: That explanation about the spark from the #3 wire is not correct.  If the light were sensing two sparks per revolution, that would throw off both the advance function and the rpm function, neither of which appear to be the case.  With the vacuum advance disconnected, the initial advance reads at the 10* point on the balancer, and I can successfully use the advance function to bring the mark back to the zero point by plugging in 10* of advance.  So I still don't know what's causing the 3* retarded reading with the vac advance connected and the light's advance set to 0.  But my hunch is that the 33* reading I get by advancing the light until the mark goes back to zero is correct.  And the rpm reading I get sounds right, but I guess I don't really know without an independent check.
« Last Edit: April 23, 2018, 06:17:59 AM by Monkey Uncle »

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #73 on: May 23, 2018, 06:01:41 AM »
Hi guys - I've been continuing to work on my issues and have reached a point where I have another question I'd like to ask the group:

Can anyone recommend a good quality Qjet fuel filter with the check valve?  I installed this filter with a valve: https://quadrajetparts.com/long-paper-carburetor-fuel-filter-with-check-valve-p-82.html

It helped reduce the fuel pressure and mitigate the overfilling/flooding issue, but after a couple of weeks the valve stuck and shut off the flow of fuel completely.  The one I used looks like a poor design in that the valve is a flat circular nylon disk.  It doesn't stay straight as it moves back and forth in its range of travel, and thus is prone to getting stuck.  A ball valve would make a whole lot more sense, but in searching online I have not been able to find a filter with a ball valve.

Stupid me thought the fuel pump had died, so I replaced the pump before it dawned on me that something might be wrong with that $2.95 filter.  The replacement pump is rated at 9 PSI max, as are all of the OEM replacement pumps that I've seen (here's the one I installed, which looks identical to my old one -- https://www.napaonline.com/en/p/CFPB0205P).  I think they are designed that way specifically to overcome the resistance of the fuel filter check valve, which is part of the OEM fuel delivery system.  So I'm thinking I pretty much have to have the check valve filter if I'm going to run a stock fuel delivery set-up.  If possible, I'd rather solve this issue with the filter than by using a non-OEM pump or re-plumbing the fuel line to put in a pressure regulator.

Thanks.

Offline roadrunnerkitten

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Re: Carb recommendations
« Reply #74 on: June 15, 2018, 12:26:02 PM »
I'm interested in any recommendations you might have for a replacement carburetor.

'78 GMC K15 chassis/drive train with an '85 C10 body
Remanned crate 350 (stock) with less than 500 miles on it, mated to an old TH350 that came from a third (unknown) donor vehicle
No emissions control equipment other than pcv hose running from driver's side valve cover into front of carb
Original stock air cleaner from the '78 truck
Carb, intake, fuel pump, and all ignition equipment re-used from the old engine
Fuel pump and fuel lines appear new

The intake appears to be the original stock intake from the '78 truck, but the carb is not.  The truck should have a 4MV quadrajet with divorced hot air choke, but it currently has a 1983 E4ME model with electric choke and several currently unused emissions features.  I am having some idle and driveability problems that were not solved by a re-build (details here if you're interested: http://forum.73-87chevytrucks.com/smforum/index.php?topic=35689.0).  It was better for a short while after the re-build, but now is even worse than before.  While it might be possible for a quadrajet expert to get it running right, I don't have such an expert available to me, so I think it's time to quit fooling with it and just replace it with a carb that is better matched to an old 350 with no emissions equipment.

From searching various auto parts websites, I see that there are remanned 4MV quadrajets available from National Reman, United, and Autoline for what appear to be reasonable prices with a 1 year warranty.  It also appears that there are several Edelbrock Performer and Holley Street Avenger models that are supposed to bolt on to my manifold, although prices for these are a good bit higher than for the remanned Q-jets.

Also my mechanic suggested that I consider a Carter aftermarket replacement with a manual choke.  I wouldn't mind the manual choke, but my searches did not find anything manufactured by Carter.  My understanding is that Carter is no longer in business, so any Carter carbs likely would be remanned, correct?

Any thoughts about any of these potential replacements?  Or any other suggestions?

Thanks.

Edit: I should explain how the truck is used.  It's a short distance errand/light to medium duty hauling truck.  Not exactly a DD since I don't use it to commute and probably drive it less than a thousand miles a year.  Although I like the cool factor of driving an old truck that is in pretty decent shape, it is not intended to be a show truck or a performance truck.  So I'm interested in a reasonably priced carb that will get me down the road with a minimum amount of fuss.
Quick fuel SL 750 vs. easy carburetor to work with very tunable. Factory adjusted to fire many scenarios


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