1981 gmc C-Class

Asked by May 28, 2014 at 08:00 PM about the 1990 GMC R/V 3500 Series

Question type: Maintenance & Repair

Hi,
Have had a 1981 C-Class RV for 3
years, and hope to actually get to
use it this year.

It has gas issues. Took it for a trip
last year, and it gave up after 2
hours. Prior to giving up, it ran great
the first 30-60 minutes. Then, any
incline, it would lurch a bit, as it was
not managing to get enough gas. So
to compensate, I would have to
release the gas pedal a bit, else it
would stop.

Got 2 hours out of town and it
stopped dead on the highway, that
took 6-7 hours to get back from. You
dreaded the sight of ANY incline!!!!

Last year - new plugs, cables,
distributor and cap, air and gas filter,
gas pump and tires. And oil change.
And bulbs. And new brakes all
around including front calipers.
This year - new gas tank and insert.

Starts good. Sounds great. Just have
to very gradually press gas pedal,
else it lurches from lack of gas
supply. Press gradually and get it up
to say, 50 kmh, and you'd never
believe there was any issues.
Boggles my mind!
Help? PLEASE
Thanks for stopping by! Any hints
appreciated.

13 Answers

77,735

Float level is the first thing to check, if it is too low you won't have enough fuel in the bowl to supply the engine under loads, then check the actual fuel pressure and delivery, sometimes it is too far for the fuel pump to draw fuel from the tank and a electric lift pump is installed back by the fuel tank to aide in supplying fuel to the front, then check the fuel tank vent system, if it is plugged then it will run until a vacuum is created in the tank that the fuel pump can't overcome then it runs out of fuel, rare but it does happen. Hope I've given you some helpful information.

Hey Tennisshoes! Thanks! A Neighbour of mine suggested the float. We discussed it and ended up considering changing carborator. I also had/have problems when filling gas. When filling slowly, fine. At gas pump, gas comes to edge of filling tube, then you watch it go down, then fill more. Have checked air vent, was fine.

77,735

The slow fill is pretty much a normal thing with a lot of motor homes I have noticed that most of the better fuel stations will fill using the second step on the nozzles, seem to work moderately well. Have you decided on the brand of carb you are thinking about?

I have no idea on the carb, I was just going to swap for a refurbished model of existing. Hope that would make the swap easier. Any suggestions/opinions most welcome. There's a place in Edmonton called warehouse services, that I've been recommended. I also believe, that the carb label broke off last year. Now what?? Thanks!

With the new gas tank, now there's a serious suction when opening gas filler cap. This normal? And I thought I had done enough of this 20 years ago! :-)

77,735

That would make it easier, but the major problem with rebuilt sis you wind up replacing it 2 or 3 times before you get a good one, Holley is the easiest to get set up but requires a far amount of work to install, Edelbrock is next, they install a little easier than a Holley but they are harder to set up but once you get they are really good. But all of them hate dirt, so make sure the filters are good. I just remembered so etching, have you checked for an in line fuel filter in the frame rail about half way down the rail, I have seen these right around the step area. Just a thought.

Hm, I can't remember looking for an in line filter. Will look. Really appreciate all the info. The RV had stood for about 13 years when I got it, so who knows what has happened. The tank and insert were very rusty. Possible some if it has moved to the carb. I have a spare fuel filter still, just incase. How hard is it to "fix/repair" float? I'm a beginner/novice level person, but like to figure stuff out. My neighbor is an ex mechanic, 28 years. I just try to bug him as little as possible, as I don't want him to start avoiding me !! He suggested if float is the issue, might as well change carb. How would I choose right card, for example, if I went with Holley? Maybe I should try the "lazy/cheap" way first? Add some carb cleaner to the gas?

77,735

I am thinking you may have a quadrajet but I really need to know if that is what you have before I can give you pointers on the carb.

It's a four barrel for sure. I'll try to get more info this weekend.

77,735

OK

So, update..... New gas tank AND new carb, finally running. Had to adjust idle, as it kept on cutting out at junctions. All that's left now, is to figure out all the inside things ( cooker, Wc, fridge) Thanks again for your time and help!

77,735

Good news then.

Hi, just Wanted to thank you again. The update so far, after two trips . The first, the idle on the new carb was too low, so at slow speeds, or turning through an intersection, it would stall. The second trip, the idle was too high , jerking when put in drive. The sound of the engine is like the choke doesn't switch off, that's the level of idle. Hope to get that adjusted tomorrow. Hope you've had a good summer! Regards, Aziz

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