Rebuilt Monojet, dies when stopping moderately hard

[Superdrag67]

As the title says I just rebuilt the monojet and also replaced the float. It runs and idles great, much better than before. The problem is that now it dies anytime that I come to a stop and have to push on the breaks harder than normal. Even normally I can kinda feel it miss a little like the engine wants to die. I adjusted all the specs according to the little sheet in the rebuild kit. My guess is the float needs to be set higher but I'm not sure. And I'd prefer not to tear it apart more than once (if possible) to fix the problem so I thought I'd ask here first to see if anyone has any ideas. Thanks in advance!

[Wrenchbender Ret]

2 ideas. The power brake unit may have a bad diaphragm.
The float level may be too high.

[PanelDeland]

Or a vacuum leak.

[mechanicalman]

Originally Posted by Superdrag67

As the title says I just rebuilt the monojet and also replaced the float. It runs and idles great, much better than before. The problem is that now it dies anytime that I come to a stop and have to push on the breaks harder than normal. Even normally I can kinda feel it miss a little like the engine wants to die. I adjusted all the specs according to the little sheet in the rebuild kit. My guess is the float needs to be set higher but I'm not sure. And I'd prefer not to tear it apart more than once (if possible) to fix the problem so I thought I'd ask here first to see if anyone has any ideas. Thanks in advance!

What they said. Also, while sitting still idling, try pushing on the brakes moderately and hard to see if it has any effect on idle, and if it causes any noise like air leaking (vacuum). It should make no difference whether the truck is moving or not for the vacuum booster to lose vacuum if it's leaking. It can leak from the diaphragm like already stated or the "power piston" in the center of the diaphragm.

That being said, if your float is set correctly then there is no reason why YOUR float needs to be higher when everyone else's do not. I doubt a foam float would be bad enough right away to sink, but if the new one is brass then maybe it has a leak.

Critical question: Did you rebuild the carb and replace the float for this reason or did it NOT have this particular problem before you rebuilt it?

Ask yourself, did the problem "create itself"? (Part or unit failure).

OR

Did I create it, and what did I do to create it?

[Superdrag67]

Thanks for the replies everyone! Forgot to mention that I do no have power brakes, so that wouldn't be the issue. I guess I could still have a vacuum leak elsewhere though? One of the vacuum caps didn't fit real tight but I don't think that would be the issue.

I didn't have this problem before rebuilding the carb. I rebuilt the carb because one day when parking the truck I had a bunch of gas flooding out of the carb. I don't know if that was the first time or just the first time I caught it. Anyways I figured rather than try and take apart and clean a crusty old carb I would just rebuild it. I'm glad I did because there just plenty of junk floating around inside it and it honestly just idle and run much smoother now. It is a new brass float.

I'll double check float level and see what it's set at.

[mechanicalman]

Originally Posted by Superdrag67

Thanks for the replies everyone! Forgot to mention that I do no have power brakes, so that wouldn't be the issue. I guess I could still have a vacuum leak elsewhere though? One of the vacuum caps didn't fit real tight but I don't think that would be the issue.

I didn't have this problem before rebuilding the carb. I rebuilt the carb because one day when parking the truck I had a bunch of gas flooding out of the carb. I don't know if that was the first time or just the first time I caught it. Anyways I figured rather than try and take apart and clean a crusty old carb I would just rebuild it. I'm glad I did because there just plenty of junk floating around inside it and it honestly just idle and run much smoother now. It is a new brass float.

I'll double check float level and see what it's set at.

If the float level is good (not too low) then take the float out and see if it has any gas in it.

[Superdrag67]

Bumping this back up top to see if anyone else has any ideas. Finally had some free time today and I messed around with the thing for 4 hours today with no changes. So frustrating!

I lost track of how many times I had the carb apart. Right now it's set right about factory specs for the float level. Still dies when coming to a stop. The float does not have any gas in it. I adjusted the float probably 6-8+ times (up and down) and no matter where the level was, the problem did not go away. Though how quickly it would die and how hard I had to hit the brakes to cause it to die did seem to change some as I adjusted.

Also the truck fires right back up after it dies, doesn't need to crank or anything. Also it will stay running if I use one foot to give it some gas while breaking so I don't see how it's anything other than a fuel issue.

Metering Rod adjustment seems to be right on. Messing with the Idle mixture screw also had no affect.

I threw away all the old stuff but I did change the jet to the new one that was in the rebuild kit. I didn't look to see if they were identical, could this be a problem? Also I'm adjusting the carb based on specs provided in the spec sheet with the rebuild kit. I'm just using the one for the year/engine of my truck. Or is it really more carb specific? What if the carbs been changed?

Can't find any vacuum leaks. Vacuum advance seems to be working right though my timing mark on the harmonic balancer shows on the opposite side of the timing tab when I try to check timing. Not sure if the HB was replaced or the rubber slipped or what.

I'm going crazy here!

[mechanicalman]

Originally Posted by Superdrag67

Bumping this back up top to see if anyone else has any ideas. Finally had some free time today and I messed around with the thing for 4 hours today with no changes. So frustrating!

I lost track of how many times I had the carb apart. Right now it's set right about factory specs for the float level. Still dies when coming to a stop. The float does not have any gas in it. I adjusted the float probably 6-8+ times (up and down) and no matter where the level was, the problem did not go away. Though how quickly it would die and how hard I had to hit the brakes to cause it to die did seem to change some as I adjusted.

Also the truck fires right back up after it dies, doesn't need to crank or anything. Also it will stay running if I use one foot to give it some gas while breaking so I don't see how it's anything other than a fuel issue.

Metering Rod adjustment seems to be right on. Messing with the Idle mixture screw also had no affect.

I threw away all the old stuff but I did change the jet to the new one that was in the rebuild kit. I didn't look to see if they were identical, could this be a problem? Also I'm adjusting the carb based on specs provided in the spec sheet with the rebuild kit. I'm just using the one for the year/engine of my truck. Or is it really more carb specific? What if the carbs been changed?

Can't find any vacuum leaks. Vacuum advance seems to be working right though my timing mark on the harmonic balancer shows on the opposite side of the timing tab when I try to check timing. Not sure if the HB was replaced or the rubber slipped or what.

I'm going crazy here!

Disclaimer: Don't try this on a crowded street LOL
Question: If you were to give it just a little throttle while you are braking, will it still die?

I'm thinking if a little throttle keeps it from dying, you might have a fuel pump not keeping up at idle.

I used to have a Ford 6 cyl that would die turning left, rebuilt the carb, found no problem, did not fix it. Then, put in a new brass float but made no difference. Found out it was a problem with the factory style float design, installed a new Ford updated design float (different configuration) (not brass, composite foam) and it fixed it.

I recommend you get a GM float, maybe a similar problem to what I had. Also, did the kit come with a clip to hold the needle valve to the float itself to prevent sticking?

Not sure you can still get a new GM float for that carb. If you can't get one, try a new composite one.

Composite (foam) floats actually work better. Lighter, float better. Got a bad rap as some early ones would get fuel-logged but newer ones are good.

[barmanvarn]

Rebuilt my first carb last week (another Monojet). Fires up fine. Can't drive it yet because, no brakes.

Subbed, in case I run into this at some point.

Hope you figure it out. Good luck!

[truckdude239]

Auto or manual? Wonder if the torque converter not letting going

[Superdrag67]

It's a manual.

Mechanicalman - Appreciate all the input in this thread. I had ruled out ignition issues because if I pull the choke on the carb or keep my foot on the gas while braking it won't die. Those two things make me think it had to be fuel related. Otherwise I would dig into the ignition side of things. To me that says that somehow it's starving for fuel under hard braking or at least that's what I think but I'm far from an expert. Yet it dies so fast I have a hard time seeing how it could be fuel either. I'm just totally baffled and frustrated.

There really is so very little to a monojet I just don't see what could be causing it. My only other thought would be to take the carb back off and take it to someone who can soak the whole thing for me. Maybe the carb cleaner and compressed air isn't getting a chunk out somewhere.

I don't know anyone with a similar truck. Thinking about finding another monojet locally and swapping it out to see what happens.

[Superdrag67]

One other question. I had ruled it out as being an issue based up what little I could find on the net but at this point I'll look at anything.

My monojet doesn't have a idle vent on top of the air horn like I see in a lot of monojets. However I noticed that not all monojets have them. Is it there on particular monojets or used in certain cases? Mine does have the hole but there is just a plug there that looks factory. Same as the plugs i've seen in other pics that I assumed were stock carbs.

Is that something that is used with the automatic choke or something? I honestly have no idea what it's supposed to do. I'll get some pics if needed.

Not my carb, just a pic from the web. That big slotted screw on top is the idle vent. Mine is plugged.

[barmanvarn]

Mine had an automatic choke and also has a plug where the vent hole is. I noticed this when doing my rebuild last week.

I had asked my Dad if it was like this from the factory, but he wasn't sure. I'm guessing it was.

I doubt that helps, but figured I'd tell you what I knew.

[Superdrag67]

Just thought I would update the thread in case someone has similar issues in the future. Happened to pick up a gallon can of carb cleaner from a friend so I pulled the carb off, disassembled and let it soak for 2 days. Flushed off and blew out with compressed air and put it back together.

Problem solved! I guess something was stuck in one of the passages.

Pretty happy about this. Unfortunately life happens and I put the truck up for sale so probably won't enjoy it too much longer.
I've learned tons from this forum, so much good info on here.

Look at that happy face!

[mechanicalman]

[QUOTE=Superdrag67;7080183]Just thought I would update the thread in case someone has similar issues in the future. Happened to pick up a gallon can of carb cleaner from a friend so I pulled the carb off, disassembled and let it soak for 2 days. Flushed off and blew out with compressed air and put it back together.

Problem solved! I guess something was stuck in one of the passages.

Well you showed some amazing "sticktoit-tiveness"

You saved her, too bad you have to her go.

I'm sure you know that carb Inside and Out!

Here, here, to the MONOJET KING!