Rough idle

[stevef]

Been reading thru Cliff's q-jet book and did some searches here for the answers, and got some ideas. But thought I'd ask anyway.

Factory stock #17059253 Olds q-jet on a 403 Olds from a 79 TA. I put a stock kit from Cliff in it a couple years ago and it ran fine on the stock 403. Recently I put the mild Edelbrock Performer cam and regular Performer intake on the otherwise unchanged 8:1 compression engine. Being that the cam and intake are only mild upgrades, I thought the carb would work fine.

The engine is on a stand where I did my cam break-in and now I'm doing my final adjustments. It starts fine and throttle response is good, but the idle is rough. The best idle I can get is around 850 rpms, but the rpms fluctuate up and down by 50 rpms, so it's like a rolling idle, not smooth and steady. It will idle lower, but not very well. I have the idle mixture screws out 5 turns, which is where it runs best and ran best before, but screwing them out further makes no difference. Screwing them back in just deteriorates the idle, and it will die if one or the other is screwed all the way back in.

Holding my hand over the primaries increases idle rpm by 200 and it becomes steady. So, from what I've read, it looks like I don't have enough idle fuel and will have to modify the idle system? In the book, it looks like your first example of a mild 350 might be comparable for a recipe for me to follow. Is that correct? I guess I need to get a set of the numbered small drill bits for the measuring and modifying?

Any advice you can offer would be appreciated. Thanks! Steve

[Cliff Ruggles]

With that carburetor number do not open up any airbleeds anyplace.

Install or open up the idle tubes to .037", and DCR's to .055".  If still using the hot air choke do not add any idle bypass air. 

I would also replace the K metering rods with our full tapered .044" metering rods, and retain the stock .073" main jets.

Install our light blue power piston spring, and it should be flawless.....Cliff

[stevef]

Hi Cliff,

Thanks for the great advice! I'll order the parts tonight. The hot air choke still works well so I won't have to do the idle bypass air then. I'll get a new kit too and go back through it all again.

Another little thing is that the throttle has a sticky spot. It looks like as the accelerator pump goes about 1/2 down there's a little resistance, like a tight spot in the middle of the travel that I can feel at the throttle lever and gas pedal, and then it continues down smoothly. Any idea what could cause that?

And lastly, I need to get some of the numbered drill bits. What is the number range that is used for this purpose? I've seen some kits that are numbered 61 to 80 but don't know if that's the right range or too small. And I'll need one of those pin vices. I see a lot of cheap bits and vices out there. Are they good enough or is there a type or brand that would work better? I have several q-jets I'll be rebuilding eventually.  Steve Fountain

[Cliff Ruggles]

The sticky throttle is a bad accl pump, we see this a lot on this new fuel.

For q-jet work you will need 61-80 and 1-60 bit sets.....Cliff

[stevef]

Thanks!

Also, I wanted to make sure I don't have a vacuum leak that might contribute to the fluctuating rpms at idle, before I do anything to the carb. The engine is still on the test stand, with the q-jet on it. So, I did a smoke test, blowing some smoke into the intake and carb. There are no leaks on the intake, but I found 3 leaks on the q-jet, but don't know if they are significant. So, I thought I'd ask if these are anything that would cause a problem. Below is a pic of one of my q-jets for showing the places where the carb on my engine is leaking.
The #1 spot is around the secondary air flap linkage. Quite a bit of smoke escaped from that spot. But being up close to the top of the carb, I was thinking it wouldn't affect much.
The #2 spot is the driver side secondary throttle plate shaft. There was some smoke seepage there, but I don't know if that has to be air tight.
And the #3 spot is where I got a small plume of smoke coming out of the accelerator pump bore.
So, do you think these would require any attention? Thanks.

   

[Cliff Ruggles]

Make sure to re-index and center the secondary throttle plates while it's apart.  The plate or plates may be open slightly, and they need to be fully closed and sealing off the bores or you will have a leak in that area.....Cliff

[stevef]

Okay, thanks again!