Cold start issue

[BDC90]

Old Q-jet 1971. Runs good idles good starts when warm right away. Cannot get it to start cold without a tiny sprits of fast start. Carb rebuilt , settings double checked. There is some primary shaft play but it returns to 650 rpm when I let of the throttle. Is rebushing the shafts really gonna fix this? It doesn't seem like that little bit a vacuum leak would have that much negative affect with choke on during cold start. Anybody got any ideas? Accelerator pumps down both holes (4MV) , no hesitation when the throttle is blipped.

[geezer#99]

When you first pump it to give it some fuel and set the high idle, is the choke closing all the way?

[71CHEVYSHORTBED402]

Originally Posted by geezer#99

When you first pump it to give it some fuel and set the high idle, is the choke closing all the way?

That was my first thought.

Does the OP have the original cold start system, thermostatic air cleaner, riser, divorce choke and such?

[RustyPile]

If the choke is closing all the way, my first thought is metering well plugs are leaking..

[BDC90]

Originally Posted by 71CHEVYSHORTBED402

That was my first thought.

Does the OP have the original cold start system, thermostatic air cleaner, riser, divorce choke and such?

All original so I'll double check the choke blade. The well plugs are the later style so pretty sure they don't leak.

[BDC90]

Re-adjusted choke arm, it may have been a little off but blade closes completely now. Truck started. Later that day (7 hours) truck started. Today truck no start. It's gotta be combo of 54 year old thermosatic coil and worn primary throttle shafts. It takes a long time before the coil will let the idle speed drop. The truck runs great after it starts and starts right up when warm.

[geezer#99]

Describe your cold start procedure.

[BDC90]

Truck in neutral gas pedal to floor, let pedal up and turn key.

[geezer#99]

Pump it twice.
Once might not deliver enough fuel.

Another thing that helps is more timing.
What’s your initial timing set at?

[Wrenchbender Ret]

Pump the gas pedal as you crank it when cold. The accelerator pump pulls off the bottom of the fuel bowl. As soon as the gas gets to the bowl the accel. pump will prime it & it will start. When engine is warm after setting a while hold the gas pedal down while cranking to clear out any flooding from percolation.

George

[BDC90]

Timing is set at specs from the manual +4 I think? The double pump worked today so I'll keep doing that until it doesn't. Waiting for the antique plates so We can start driving it.

[71CHEVYSHORTBED402]

When my truck's cold, I nearly always have to start it by procedure, twice. Perhaps I should add, with the key on one engine turn-ish. I'm no expert, it only takes a second. Rebuilt carb., almost fresh everything and tune.

[BDC90]

Well that would have been a handy sticker to have. This truck has the instructions for the PTO winch in that spot. Of course We do not have an owners manual either. Yet.

[Rust_never_sleeps]

re-bushing the q-jet is not a big job, and it does make idle/choke/mix more predictable. Hard to know how much difference

I wish I had a sight glass in mine, cuz knowing if the bowl is full when working alone makes for less guesswork about pumping the pedal

[71CHEVYSHORTBED402]

Originally Posted by BDC90

Well that would have been a handy sticker to have. This truck has the instructions for the PTO winch in that spot. Of course We do not have an owners manual either. Yet.

I have one, but can't bring myself to install it on a perfectly good visor. I don't think my 71 had one. Didn't have one when I got it in 89 anyway. Ha ha, I just looked at the date on those instructions, my May 1971 truck didn't have that decal.

The instructions say start a warm engine with the pedal halfway down. I've never had to do that (402, 4Brl, 400TH). I don't hit the accelerator at all, and starts right up.

I've never had to crank it per extreme cold instructions.

[BDC90]

Late update. Spent yesterday using Cliff's High Performance throttle shaft bushing kit. truck starts right up with 2 pumps on the pedal.

[PanhandleShantyman]

I'll second geezer#99's comment about more base timing. If your truck has rusted/frozen vacuum advance like mine, it'll go a lot better with +12 or so to initial timing.

When I first got my truck I spent so much time fiddling with/worrying about carburetor bogeymen, but as I learned more I realized almost every problem I had could be solved with a timing light. Vacuum gauge sorted out the rest of it. Almost everything I did with my carburetor (except for cleaning out debris) was unnecessary.

One exception, when I got it the choke was straight out WIRED into a mid position because the thermostatic coil was busted, it did start better when I made the choke functional again. It just required replacing the auto choke part. That was a pain because on my '69 the auto choke assembly bolts in around that oven coming off the exhaust and it was super corroded and the bolt snapped off and I had to drill it out. But in theory anyway, not a complicated fix...

anyway yeah I'd echo that if the choke works and the timing is set with decent advance, for my old truck that and a new set of spark plugs was all it took to fix the cold start problems.

[Rust_never_sleeps]

Originally Posted by BDC90

Late update. Spent yesterday using Cliff's High Performance throttle shaft bushing kit. truck starts right up with 2 pumps on the pedal.

Nice. I did mine as part of a rebuild, so I couldn't tell how much improvement came from that piece, but it was pretty sloppy