Zenith rebuilt. No power past 40mph

S

steward614

Junior Member
Greetings. I am a jewelry who used my ultrasonic and steam generator to clean and inspect (10x magnification) a few old zenith carbs, pieces and parts to make two good units. The two run really well, new gaskets, i set the float but i did not perform a flow test for lack of equipment. Of the two carbs one has little power beyond 40mph, when i accelerate i hear the vacuum but just doesnt have the oomph. Might there be a chance that i do not have enough volume of fuel in the bowel? I shrived to adjust to 5/8" fuel level from the top however that took two gaskets to set the float needle to get the adjustment. No popping or backfires. So i dont believe its a rich flow issue. Any advice?
 
Utopia- I did turn the GAV open up-to two turns then back down to damn near off. Not a substantial change. All while running 40mph made an impact when open, some popping.
 
Mitch- I read the attached link to the main jet artificial on rebuilding. Appears to address my issues with high speed power. Without flow testing I am left with purchasing calibrated jets. I didnt know if there was an additional testing method while performing under load.
 
Mr Miller, good point. I recently replaced dist., points and cap and button. All adjusted to spec along with TDC of #1 on contact. Let me let her cool off tonight and Ill check the timing.
 
Check your point gap and ensure it is within the specified 0.018-0.022" range. Going outside of that range affects timing and results in poor performance. Make sure the indent on your timing gear is centered exactly in the timing pin hole, too. (I know you asked about Zenith carbs, but like the guys say make sure your timing is spot on.)
 
If I understand you correctly, you have two carbs; one runs great, the other runs great below 40, but gives you trouble above 40. If that is correct, it would suggest that the problem is not ignition. If is was, you would experience the problem with both carbs.

I would agree that the likely culprit is a problem jet. I would suggest this... swap out the jets from the 'good' carb to the 'bad' carb. If that solves the problem, it would confirm that it is one or more bad jets.

If you do buy new jets, I agree with Mitch, get the ones from Renner.

Good luck,

Ken
 
forever4 said:
How did you clean the passages in the lower casting? Ultrasonic alone will not be reliable. I use electrolytic derusting, a Branson ultrasonic tank, and mechanical tools.

Two float valve gaskets is one too many. Your fuel level will be low. Did you remove the secondary well when you cleaned the casting?

The problem with many carbs is that they are not nearly as clean as they look, or as people think. I just did 8 more Zeniths on Sunday, and it took an entire afternoon to clean them all properly.
Click to expand...

If you had that new GAV socket you could have done the job in half the time.:D
I'm still waiting on mine also.:)
 
forever4 said:
Actually, I just encountered the very first 7/16 hex GAV which I believe is original, not an old repro. It was on a Zenith 1 casting. The entire rest of the carb was an unmolested original, no signs of any tampering or previous disassembly.
Click to expand...

Yep, I had one or two of those about 10 years ago, and also thought it was original.
 
KGBnut said:
If I understand you correctly, you have two carbs; one runs great, the other runs great below 40, but gives you trouble above 40. If that is correct, it would suggest that the problem is not ignition. If is was, you would experience the problem with both carbs.

I would agree that the likely culprit is a problem jet. I would suggest this... swap out the jets from the 'good' carb to the 'bad' carb. If that solves the problem, it would confirm that it is one or more bad jets.

If you do buy new jets, I agree with Mitch, get the ones from Renner.

Good luck,

Ken
Click to expand...


That's how I read it also....
 
forever4 said:
How did you clean the passages in the lower casting? Ultrasonic alone will not be reliable. I use electrolytic derusting, a Branson ultrasonic tank, and mechanical tools.

Two float valve gaskets is one too many. Your fuel level will be low. Did you remove the secondary well when you cleaned the casting?

The problem with many carbs is that they are not nearly as clean as they look, or as people think. I just did 8 more Zeniths on Sunday, and it took an entire afternoon to clean them all properly.
Click to expand...


Morning-I used the heated ultrasonic and each passage was blown out with 70psi of steam (a steam boiler we use in the Jewelry industry which has a fine tip outlet) and yes all jets were removed, cleaned and inspected. As for the float valve gaskets_ i added the second one to get the proper height of fuel in the bowl when the valve shuts off. However there may not be enough fuel once it gets both jets flowing at high speed...
 
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