Author Topic: Power and towing.  (Read 2394 times)

Offline buddeboy89

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Power and towing.
« on: September 19, 2017, 11:48:11 PM »
 So this is something that was going on with my old 86 k10 along with my 77 k20 in currently own. When the truck doesn't have any load or anything on it it seems to run pretty decent but doesn't seem like it'll get over 70 to 75 mph and definitely not very quick. It'll get up and go off the line fairly good but pretty slow after that. Then today I had to tow a car trailer with a Tahoe on it and it seem like it towed worse than my other truck with a wimpy 4.8 in it. It took forever and I mean forever to get up to about 55 miles per hour and wouldn't really go past that. Getting on the on ramp to the highway it seems like it didn't even want to gain speed. And then when it was in 3rd gear on the highway it seems like it was really hard to keep speed and almost sounded like a squealing like a belt was slipping or maybe some kind of squealing from the transmission or something. The long story short is I figured a k20 would have no problem towing something like that but I was almost afraid I wouldn't make it. It had a 400 with a th350. 14 bolt rear. 10 bolt front. New plug wires. Going to check plugs and distributor tomorrow. But seems to drive pretty good, not great, but good when there's no load. Any help would be greatly appreciated.

Offline 75gmck25

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  • 1975 GMC K25 Camper Special, 350/TH350/NP203
Re: Power and towing.
« Reply #1 on: September 20, 2017, 01:43:40 PM »
A couple of things to check:

Base+Mechanical+vacuum advance timing should not exceed about 54 degrees.
- Recommended base timing is probably 8 degrees, but you can usually use 12 degrees, and it may even work at 16 degrees initial.  More base timing will help the power.
- Check to see that mechanical advance kicks in another 18-20 degrees, preferably not later than 2500 rpm.  That means that at a working RPM you should have 30-34 degrees of advance.
- While working on the distributor, also verify that you get about 18-20 degrees more from the vacuum advance.  If you advance base timing quite a bit and it runs well, you might have to limit the vacuum advance to avoid pinging at highway speeds.

Verify that the throttle cable is adjusted properly and it pulls the carb linkage fully to max throttle.  Its a simple adjustment, but if its wrong you may not be getting the secondaries to kick in. Also verify that the TH350 kickdown is working.

The squealing may be the alternator belt, since its turning both the fan/water pump and the alternator.   What kind of fan do you have?  A stock clutch fan should freewheel at high speed, but a fixed fan would still be coupled to the engine, which might make the belt slip.  The alternator causing belt slippage is usually not an issue unless the battery is run down and the alternator is still trying to keep up the voltage.

Bruce

Offline buddeboy89

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Re: Power and towing.
« Reply #2 on: September 21, 2017, 07:30:27 PM »
Thank you. I'll look into the things you suggested.