Carb Q&A

Doug D. · Jun 23, 2013

I'm thinking about changing carbs. Currently, I'm running a 1600 dual port with a Bocar 34PICT3 carb. Standard 4 speed IRS trans, standard ignition with a dual vac distributor.

I mostly ride rural two lanes, with some interstate time thrown in on longer trips. I'm getting decent gas mileage (25-30 depending on conditions). It has plenty of power for just knocking around, though it seems a little sluggish on the top end, especially on the interstate.

I'm considering a Weber 32/36 Progressive set-up with hopes that it'll improve top end performance without compromising fuel mileage. Any input?

Rsw · Jun 29, 2013

What and how do you have your timing set at? Are there any flat spots/sputters in the motor at a certain rpm? Sorry for the slow reply, cumputer been messing up.

Doug D. · Jun 29, 2013

Last time it was set, I didn't have a light, so I had my bug mechanic do it while I was working on something else. I think he set it around 25 degrees BTDC. Like a dumbazz, I didn't think to ask. I know when I had a 009 distributor on it, it was advanced as far as it would go, and we backed it off a bit when I put the dual vac distributor on it. It does have an intermittent flat spot in the low to mid range. Not bad, just an occassional sputter.

Rsw · Jun 29, 2013

Might give it a little more timing. Should be set at 28 to 30 btdc at around 3000 rpms. I did away with my dual advance distributor and went to a cheap China mechanical one. Still has a flat spot in the low to mid range under a hard pull. No problem with with top end power out of my 34 pict-3. Just mess with it a little till you find the sweet spot in the timing. Do you have a degree pully on it?

Doug D. · Jun 29, 2013

Thanks, I appreciate the information! And yes, it does have a degree pulley, though it's pretty worn and a little hard to read.

Rsw · Jun 30, 2013

When you say "dual vac distributor" does that mean you have 2 vac lines on the distributor?

Doug D. · Jun 30, 2013

Yeah, I think dual advance is the correct term.

Rsw · Jun 30, 2013

If it has 2 vacuum ports on the distributor, I think those were made for automatics. It should be a vacuum advance/vacuum retard. You just need to run the advance side of it. I paid over $200.00 for a bocsh dual advance distributor. It is a mechanical and vacuum. They are called a 034. They were made to take the flat spots out, but it made mine worse. I put the cheap China mechanical back in and it runs twice as good. I think it's because the rpm's come up quicker on a trike then they do on a heavier car.

pafree · Jul 1, 2013

this link may help. Distributor Vacuum Hoses - Where Do They Go?

pafree · Jul 1, 2013

Doug D. said:
I'm considering a Weber 32/36 Progressive set-up with hopes that it'll improve top end performance without compromising fuel mileage. Any input?

people either love them or hate them. research on proper setup and you will have a good carb but it will take some fiddling to get it right.

Rsw · Jul 2, 2013

To answer your original question. The 34 pict3 works out mathematically enough carburetor for motors up to 1680. If it is right, you wont gain much by going to a Weber progressive except headaches. If the carb is in good shape and working properly, I would still say your top end power problem is in the timing/distributor.

Rsw · Jul 2, 2013

pafree said:
this link may help. Distributor Vacuum Hoses - Where Do They Go?

Good info!!

Doug D. · Jul 4, 2013

Thanks, guys! I appreciate the great info. Padfree, that's a great article.

I have a four day weekend, so I think I'll spend some time messing with the timing and checking my lines. You guys may have saved me a nice chunk of change on this carb changeover! ThumbUp

hawkeyefxr · Feb 14, 2016

Well i an nearly 3 years late on this

but it may help someone else.
I had a weber on my Trike when i bought it and i thought great. How wron was i, plugs that lasted about 50 to 100 miles before fouling, fuel consumption of a V8 !.

I did discover a few things out about the weber card, A guy that has worked with Weber's on VW said he has never seen one that came jetted right and he had never seen two jetting the same. To get it tuned right it needs to go on a rolling road, cost here in the UK £200.00 around $300.00 i think

I replaced the Weber with a Solex 34 pict 3after a quick setup it ran beautifully.