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Discussion Starter · #1 ·
I have a 1679cc with a Weber progressive carb. I just rejected it to some specs from a guy. I installed on the idle 50 from 60 on the main. On main jets 137 to 125 and 180 and air jets 160 n 180. I got it running and it idles smooth but now when I rev up it still has a slight hesitation that I just can’t get out n on the idle back down a small pop sound from the exhaust. The reason I changed the jets is because for it to idle smooth the mixture screw had to be closed n I know that ain’t right. Now I’m not sure where it’s at but questing it’s maybe a turn or so out which is better than before. So any ideas on what I need to do. Oh and the 88mm pistons are thick walls with the 90.5mm heads on it.
 

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So if you mash the throttle is there a flat spot.. This can be a single carb thing. The carb is too far away from the plugs. Twin carbs don't do this as a rule. Are the pre heat pipes hot. Is the manifold under the carb cold. A 009 dissy can cause hesitation too. You could try 1 size smaller idle, but the smaller you go the more chance of it getting blocked. Check the colour of the plugs after a run
 

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You may have already come across these, but another two helpful web pages on the matter:


The second talks to air-fuel ratio adjustments (calibration) at the bottom, regards correct number of turns and jet sizing.

I've just fitted one to a new (top end build) 1641. I've followed the jetting advice of the link DK Bug provided, as a starting point. I've tried also to find a preheated manifold (in the aircooled link) but they're v hard to locate nowadays. Others run a pipework/hosing from the exhaust side of the tinware to the air filter inlet to compensate, for limited heating from a standard preheat manifold. I've not taken that route as a start point, but I've also not started my engine yet.

Linkage is an ass with these too, I've fabricated/bodged this (home build style)

Motor vehicle Automotive tire Gas Auto part Engineering


As I say, not fired mine up yet. Given the stories you hear of running/tuning these carbs I'm as nervous as I am excited about the day I turn the key - v soon now.

Good luck with your endeavours.
 

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Discussion Starter · #5 ·
So if you mash the throttle is there a flat spot.. This can be a single carb thing. The carb is too far away from the plugs. Twin carbs don't do this as a rule. Are the pre heat pipes hot. Is the manifold under the carb cold. A 009 dissy can cause hesitation too. You could try 1 size smaller idle, but the smaller you go the more chance of it getting blocked. Check the colour of the plugs after a run
It didn’t have this problem before I changed the jets but that’s because the mixture was closed off and according to specs it needs to be 1 to 1.5 turns out. Yes the heat tubes are hooked up. Had to modify my Baja exhaust to get it to work.
I am not an expert on the issue, but as I have been thinking maybe to fit a Weber progressive to my engine, I have done some research and came upon this article.
There seems to be some well founded suggestions in there.

Making the Weber Progressive Carburetor (32/36 DFEV) Work on the Aircooled VW Engine | VW Parts for Aircooled Volkswagens - Aircooled.Net
that’s where I went n got the information for changing the jets.
 

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Discussion Starter · #6 ·
You may have already come across these, but another two helpful web pages on the matter:


The second talks to air-fuel ratio adjustments (calibration) at the bottom, regards correct number of turns and jet sizing.

I've just fitted one to a new (top end build) 1641. I've followed the jetting advice of the link DK Bug provided, as a starting point. I've tried also to find a preheated manifold (in the aircooled link) but they're v hard to locate nowadays. Others run a pipework/hosing from the exhaust side of the tinware to the air filter inlet to compensate, for limited heating from a standard preheat manifold. I've not taken that route as a start point, but I've also not started my engine yet.

Linkage is an ass with these too, I've fabricated/bodged this (home build style)

View attachment 303298

As I say, not fired mine up yet. Given the stories you hear of running/tuning these carbs I'm as nervous as I am excited about the day I turn the key - v soon now.

Good luck with your endeavours.
Thanks I’ll look into it. I had one on my old Baja I had yrs ago. It was a 1600 stock. And it worked like a champ. Almost pop the front tires off the ground. I’m thinking maybe the older carbs where built better then the new ones.
 

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You've ran it rich with bigger jets. Now that you've weakened it off with a smaller jet, it's exposed a hesitation. The hesitation is either lack of fuel or a cold manifold etc. You say the pre heats work, so that leaves a lack of fuel. You might fix the hesitation with a bigger pump jet. You could use a micro drill bit to enlarge the 1 you already have.
 

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Discussion Starter · #8 ·
You've ran it rich with bigger jets. Now that you've weakened it off with a smaller jet, it's exposed a hesitation. The hesitation is either lack of fuel or a cold manifold etc. You say the pre heats work, so that leaves a lack of fuel. You might fix the hesitation with a bigger pump jet. You could use a micro drill bit to enlarge the 1 you already have.
Well I got it a lil better what I did was opened the mixture screw some more the hesitation is better but I can smell a lil gas as I rev it up n it comes down. I know vw engines need a lil rich to run cooler If this doesn’t get better I’ll try your way.
 
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