Power Loss After Carb Rebuild
 

Just rebuilt my Zenith carb because of an intermittent loping idle and loading up/stalling while stopping. It still had original Zenith jets in it and the tip of the cap jet looked like it got bent while the carb was disassembled at some point. It is an early carb that has the brass GAV seat and didn’t have a gasket under it so that was a big part of my problem, I’m sure. The float was set according to the specs in Les Andrews’ book but in an effort to control the stalling at stops, I lowered the level 1/8”. Started it up and got everything adjusted in and it made a huge improvement in lower rpm smoothness and idling. Only trouble is trying to accelerate and climb hills. You notice it just pulling out of the driveway that it just doesn’t want to rev. It feels just like a tractor with a governor on it, will run smooth all day at part throttle but when you put your foot down, there’s nothing there. Almost seems like the main jet isn’t flowing at all or very little. I compared the orifice hole sizes on the new and original jets and there’s almost no difference so I’m stumped. I also replaced the fuel line and screen in the sediment bowl at the same time so it doesn’t seem likely that it got a particle in it that could clog the jet already. Doesn’t seem likely either that lowering the float a bit would make it act like this either. I would think it would starve for fuel, then recover when you let off the throttle, then gradually starve out again. Any thoughts?

Re: Power Loss After Carb Rebuild
 

probably crud restricting cap comp or main jet .... did you clean the passages .? a blast with an airline may solve it , if not time to take it apart again! lots of info on this website , particulalry article on carb rebuilding by Tom Endy

Re: Power Loss After Carb Rebuild
 

Have someone mash the pedal down, look at carburetor....is it wide open?
I have found dozens of model As where wide open is only 1/2 or 3/4 open.

Re: Power Loss After Carb Rebuild
 

I did clean the passages while it was apart, screen was cleaned, fuel line from sediment bowl replaced(not inserted too far into carb),sediment bowl cleaned, and screen in the bowl replaced. It idles best at 3 turns out on the air screw which would indicate no restriction on idle jet and no air leak. High idling and low speed running are best at just over 1/4 turn open on GAV, indicating that cap and compensating jets are okay. Decelerating to stop and transitioning from open throttle to idle are nice and smooth, indicating the secondary well passages arenÂ’t blocked. That only leaves the main jet or float level. IÂ’ll probably swap the main jet back to original first to see if the power comes back. Before the rebuild it would climb hills pretty well in 3rd. Today, the same hills were a struggle in 3rd or required a downshift. The throttle butterfly opening wouldnÂ’t have changed with the rebuild but it is a valid concern with this car. The accelerator will only open the butterfly to the stop with the floor mat removed. Is there any adjustment in the linkage? CanÂ’t find any mention of it in Les AndrewsÂ’ book.

Re: Power Loss After Carb Rebuild
 

Is your throttle assembly arm bent? that bolts to rear of motor!

Re: Power Loss After Carb Rebuild
 

It looks like something in the linkage is tweaked. Possibly a combination of the arm on the throttle assembly being bent back and toward the block slightly and the linkage rod to the carb having a slight bow in it. It looks like someone put the bow in the linkage so it would clear the choke rod better. That probably means the arm on the assembly is bent in. The pedal sits fairly close to the floor (about the same height as the footrest when it’s bottomed all the way out) and seems too low. If there are no other means of adjusting, I guess it’s time to start bending stuff back into shape.

Re: Power Loss After Carb Rebuild
 

Check to see if the throttle is opening all the way first. Since you put in a new main jet, another thing to check is to see if the tip of the jet is at the throat of the venturi. If it is not at the throat it will not flow the proper amount of fuel.

Re: Power Loss After Carb Rebuild
 

And tap on the carb a bit. Sometimes that needle-n-seat /float tends to hang a bit when the carb is upside down, and such. However, it seems like you are on the right track.

Re: Power Loss After Carb Rebuild
 

Both good suggestions. When I first started the car it fired right up cold but then promptly flooded out when pulling out of the garage. Tapped the carb to free the float, held it to the floor and it cleared out. I was questioning the lengths of the replacement jets too. The original Zenith cap jet was shimmed up to match the height of the main jet with three gaskets. I only used one because the replacement was a tad longer. The replacement main jet sits slightly higher so it may be too long. It certainly looked like they were both approximately at the narrowest part of the venturi but itÂ’s not easy to get an exact measurement on that. Really all of the jets and needles in the kit were different lengths than what came out but the parts that were in there were a mix of original and replacement from a century worth of fiddling. At least I know the original main jet was giving a good mixture so IÂ’ll have a benchmark.

Re: Power Loss After Carb Rebuild
 

jet sizes with ONE Gasket!! tight! NO gasket on idle jet.

Re: Power Loss After Carb Rebuild
 

You would be wise to take a deep breath, let it out, slow down a little. You know how it ran before you replaced the jets, cleaned the passages, replaced the brass GAV seat& gasket. Not only might it be a good idea to put the main jet back in ................... it might be a good idea to put all the original jets back in. See how it runs then. If it runs the same as it did before the rebuild, YES, then you can start to blame it on the new jets. BUT, for now, focus ONLY on the carburetor until you're sure it has nothing to do with anything else you did. DO [U]NOT[/U] delve into the accelerator assembly. If the accelerator assembly worked properly before the rebuild, it should work properly now. Nothing you have done, so far, should have changed that. Good luck.

Re: Power Loss After Carb Rebuild
 

Thanks, that’s good info. What book is that from? I’ve found some conflicting information on the sizing from various sources. Most show the compensator jet as using a smaller orifice while this diagram shows larger than the main and cap jets. My carb didn’t have an original compensator in it so I can’t verify that. Both my original and replacement were smaller than the main.

Re: Power Loss After Carb Rebuild
 

I only use original jets when rebuilding a zenith, I've never been satisfied with repo jets.
Also I sonic clean all the parts.
I just want to touch on the throttle linkage because it may help someone.
The linkage on the back of the engine gets bent over the years, the front motor mount can have a effect on the linkage, as it will sag and lower the front of the engine with age.
Your hand throttle should open the carb on the first click. I know this sounds like your opening a can of worms, but if you want everything right,then you have to sort through it all.
Your not going to find this information in any of the books,just keep asking questions on the forum.
Wick

Re: Power Loss After Carb Rebuild
 

Did you check the accelerator butterfly shaft for wear? If the shaft is worn you could be pulling air in which could affect the proper fuel flow needed at the higher engine speed. With this type of leak you could be fooled by the improved lower end engine speed conditions. This condition and the suggestions made about verifying the accelerator linkage opens the butterfly completly at the full throttle position.

Re: Power Loss After Carb Rebuild
 

It is very likely that the throttle assembly got tweaked as a result of a failed front motor mount. I just recently replaced a failed aftermarket coil/rubber bushing style mount that had no rubber left in it and the motor had been moving all over the place. I did check the throttle shaft play and it was still fairly tight. The only movement I found was the butterfly being able to move slightly side to side being smaller diameter than the carb body.

Re: Power Loss After Carb Rebuild
 

If the butterfly is properly installed you should not have side to side movement in the idle position. With the linkage disconnected position the butterfly in the idle position. If it is correctly installed the OD of the butterfly will be a line to line fit with the bore of the carb.
If not, position the throttle in the idle position, loosen the idle screw completely, and loosen the 2 small brass screws that attach the butterfly to the shaft and very lightly tap the throttle shaft in either dirrection until the butterfly aligns with the bore. Then retighten the screws. This should prevent end play. If the shaft's diameter is worn there will be up and down motion which can cause intake air leakage. This can be corrected by installing a new shaft and bushings which are available from the parts suppliers.

Re: Power Loss After Carb Rebuild
 

I have bought jets that were not drilled to the correct size even though they had the correct number on them. Use small drills to measure the size. Insert the shank of the drill into the hole. Find the size that just fits and then measure the shank with a micrometer. You can buy drill indexes with small drills. If the hole is not the correct size, you can use the correct size drill to drill it out. If too large, you can solder up the hole and then drill it out to the correct size. After doing this, countersink the main get on a Zenith carburetor so that the gasoline does not weep out.

Re: Power Loss After Carb Rebuild
 

Yes, and they bend easily just from use. My car is a 28 (March) and the thing is of somewhat a different design. I finally had got tired of taking mine off to straighten it each year, and put on another one that I got from a an auction. I had 3, and I picked out the one that looked the best.

Re: Power Loss After Carb Rebuild
 

Yes, and they bend easily just from use. My car is a 28 (March) and the thing is of somewhat a different design. I finally had got tired of taking mine off to straighten it each year, and put on another one that I got from a an auction. I had 3, and I picked out the one that looked the best.

There were things on the 28 that were different...

Re: Power Loss After Carb Rebuild
 

Just posting an update on the problem I was having. Seems to have been the repro main jet was the issue. It was just a tad shorter in length than the original and the orifice was slightly smaller diameter. Also the repro drain plug had slightly deeper threads and I wasn’t sure if maybe that was causing it to sit too close to the bottom of the jet and restrict it’s flow so I went back to the original there as well. The power is back and the car runs best right at 1/4 open on the GAV. Still have a little bit of an erratic idle which I believe is from a leaky manifold gasket. I notice some fuel seeping from under the rear port while it’s idling. Is it normal to have that much fuel pooling in the manifold. It’s not running rich and it’s not misfiring so that seems strange to me.