Carb, vacuum, & timing

[Jimboss77]

I have worked through several issues recently and hopefully at my last. My engine will fire up immediately with a peddle pump and a quick rotation of the starter. Seems to be running smooth at first but as it warms up starts to ‘lope’ like a cam while at idle. Almost sounds like it will die but picks back up and continues to run. When I put it in gear (AT) it really bogs down and stutters.

77 stock 302. All emission crap removed and things blocked off. I tried adding pics......may or may not work. Distributer has vacuum advance connected to passenger side of carb. There is a port on the front of carb, driver side that is capped. PCV valve connected to rear of carb. T-fitting on rear of manifold has hose to brake booster, hose to tranny, and 3 other ports blocked off. I will start tomorrow with the simple check for cracks or leaks in vacuum system. Just want to know connections are correct. I have heard a high pitched squeal a few times that I first suspected to be PS pump. Removed the PS belt and still had the squeal primarily at rough idle, acceleration made it stop.

The carb......the fuel mixture screw on the driver side of the carb appears to have leaked fuel, wet and dark colored vs the passenger side which is clean. Also found evidence of possible leak around base gasket and did torque those 4 nut/studs and little more ~ 1/8 turn not much. I have done no carb adjustments. Just because of the leaks I’m thinking a carb kit is a good idea.

Timing.......in another thread I posted I believe the engine is from a 70’s mustang and I can’t see the damn pointer from above. Engine doesn’t ping, starts on first key turn, and runs 174-194 temp with laser temp gun on top rad hose. Feel good timing not an issue although it could be tweaked I’m sure.

Big thread I know but sometimes TMI is good.

 

[blubuckaroo]

Sounds like a vacuum leak. It may be internal or external, but it's a vacuum leak.
Check out all, external suspects first, then pull the intake manifold, and check the gasket.

 

[71broncman]

While you're checking the vacuum lines, check the vacuum advance can on the distributor for function as well. Pull the distributor cap and apply vacuum to the hose attached to the can. A MityVac or sucking on the hose works for this. You can see the lever from the can move the plate in the dist. if its good. If the can won't hold vacuum it's bad and is causing a big vacuum leak. I went through this about a year ago, and that was the problem with mine. Replaced the can and now all's well.
Mark.

 

[jckkys]

Whether you're 302 is a stock '77 Bronco engine or a "70s" Mustang engine, the long block is the same. In other words a '77 Bronco engine is a '70s Mustang engine. The difference is in the front dress or everything on the front of the engine. This includes the timing cover, water pump, harmonic damper, pulleys, fan, and brackets for the power steering pump/alternator. The timing pointer has to match the timing cover and damper. We would need a photo, to know if yours does.
As to the dying engine. It doesn't sound like your Idle speed and idle mixture were set with the engine running, as they need to be. An automatic transmission puts a load on the engine, that always slows it down when put in gear. Setting both in neutral will cause your problem. The mixture screws don't have a seal. All the air and fuel are drawn into the throttle bore so they're not needed.
A loose alternator belt is likely the source of your squeal.
Some of the '77 2150s had a small hose nipple in the front of the base, in some applications and DSOs. This was to function the EGR valve. So if you have no EGR it should be capped. The stock PCV port on '77 Broncos was in the front of the carb spacer not the carb.
The mounting nuts should only be tightened to 60in.lbs. or 5ft.lbs. of torque. Don't over tighten them.

 

[Jimboss77]

A ton of good information from y’all. Started looking for vacuum leaks and didn’t find anything obvious. I have never tuned a carb with a vacuum gauge but I had one around so I hooked it up to the tree on the rear of the manifold. Turned both mixture screws all in and back out 1-1/2 turns. Started engine (cold) choke idling up engine and the hg was bouncing from 17-20hg. Turned screws another 1/4 turn and it improved to 18-20hg. Engine still warming up and choke had it at high idle. Let it warm up and kicked the choke off and it went lower idle speed and started bouncing 17-2hg again. Started with 1/8 turn moves and have it holding 19.5-20.5 at idle. Both screws are now out ~2-1/6 turns out.when I idle up the vacuum increases to 22-23 and holds very steady. I’ll get someone to assist later and re-adjust with trans in gear. The Engine is running 90% better than before. It’s in the shop so no test drive but I shifted trans and there was no stuttering or miss.

Additional vacuum ? Currently the distributer advance is connected to the passenger side of the carb. There is another ported nipple for the old egr on the front of the carb, can I just connect advance there? No reason except I’m just a touch over the ‘ocd’ line and shorter is cleaner and more direct

Not sure of rpm but will check with a hand tach later, feels and sounds ok, not too high to cause hard thunk shifting trans into gear. I’m also gonna address my issue of not being able to see the timing pointer and marks. This past winter while repairing rad and water pump I verified mechanical 0 and added a white/ black timing tape to the balancer. Didn’t help because pointer still hidden,yadda yadda yadda. Thought is to set engine to mechanical 0, remove the tape and move to top of balancer, make and install another pointer, and cure my timing setting questions for good. Thoughts? Again thanks for all the information.

 

[jckkys]

The second vacuum nipple in the front of the carb is calibrated for the EGR valve it won't function the vacuum advance correctly. The ported vacuum nipple on the right side base of the carb is specifically designed to function the vacuum advance on the distributor. The idle mixture screws don't have a set number of turns it is just turned to give you the best quality idle on your engine.

 

[Jimboss77]

Thanks jckkys. Figured there was a reason for where the advance was connected but had to ask. I’ve never adjusted the carb since buying it 3 yrs ago, have been working on electrical and other issues, using the gauge made a big difference. I’ll continue with getting correct timing position and will check all the spark plugs. If I’ve been running rich all this time I probably have fouled one or more.

Gonna be busy next few days but I will post any new findings/info as I keep fine tuning so it may help others.

 

[jckkys]

I've adjusted my idle mixture and speed several times a year. Changes in temperature, humidity, and altitude mean the mixture has to be adjusted accordingly. You just turn them with you're fingers to get the best idle quality. The automatic choke needs to be adjusted seasonally too, at least if you want the engine to run it's best. There's no computer in the truck. It has to be in your head.

 

[Jimboss77]

Had some time today to continue tuning my carb. I did find an issue with the fast idle adjustment and my choke wasn’t closing all the way, easy adjustments. But this lead me to some more questions.......

Looking at pics and video’s (mikescarb) I can’t say for sure what carb I have. It has the squared/straight rear base like a 2150. It does not have the vacuum port on the top front like the 2150 pics I’ve seen. Besides not having the top vacuum port it also has the choke pull off device on the top plate like the 2100s I’ve found.

Is this some crossbreed built from 2100/2150 bases and tops or did ford build some with both features? It also has electric assist on the choke. If I ever rebuild this carb how will I get the correct kit?

 

[gr8scott]

This and some timing tape will fix your timing pointer issue. It bolts to the bottom left timing cover bolt, the small screw just screws into a boss on the timing cover.
Then it just "hovers" over your balancer.

 

[Jimboss77]

Thanks for the location pic gr8scott, been looking for a place to mount one. I’ve got a pointer on order along with new timing tape.

I found an old post today by RJA102 asking for help identifying his carb. His pictures are identical to my carb except no electric assist on the choke. The majority on that thread identified it as a 2100.