2F Aftermarket carb comparison (2 Viewers)

[steffan]

As they say, education is expensive.... this all came about because I finely was able to start up the engine ('72 cruiser with a '76 2F). I had purchased a new aftermarket carb from Trollhole years ago when he was selling them. It bolted up nicely and everything fit just as it should. At the time, it just seemed like a better route than rebuilding the stock one which looked very rough.
Once it got fuel it started up but ran very rough: wouldn't idle, was stumbling at higher RPM and backfiring - all symptoms of running lean, which was confirmed by my Wideband AFR gauge.
We doubt checked the timing, went through the tuning procedure etc and could get a better/ not great mixture at idle but again, as soon as rpm rose, it was stumping and leaning out. Tried everything to rule out a vacuum leak but couldn't find anything.
Based on what everyone else was saying about the aftermarket carbs, it's not unusual to have some debris in the carb/ blocked passage etc so I pulled it and tore it down to clean it.
I was super careful pulling it apart because I wanted to preserve the gasket - impossible. The gasket was some kind of fiberous paper material that must be glued on - separated on both sides.. no way to salvage

 

[steffan]

Took a long time to get it cleaned off. All the gaskets were like this: Venturi etc. I was able to get the Venturi gaskets off ok but it was a slow process.
likewise, the jet covers also seemed like they had some epoxy/ glue like sealant. This could be looked at like as a good thing as long as you don't have to disassemble it. This just meant I that after cleaning and inspecting, I had to wait a week for a new gasket to come in the mail.
Everything looked perfect inside: no dirt or debris/ all the passages were clear etc.
After install and starting up, it did run better at idle and we could get a good mixture but anything over 1200 rpm and it would lean out again.

 

[charliemeyer007]

See if you can measure the gasket thickness by measuring both sides, then scraping off the gasket and measuring again. Buy a sheet of gasket paper that is as close as you can get.

 

[steffan]

All this is a long way to say, I ended up purchasing a new, made in Japan Fuji carburetor. My thought process was this: pleanty of people have wrote about the the hit-or-miss quality control on these carbs. Having exhausted all my searching for a vacuum leak I came to the conclusion that the carb must be defective. Like I said, education is expensive - I put the new fuji carb on and had exactly the same symptoms
Looks like I'm going to be swapping out manifold gaskets this week in search or a vacuum leak.

 

[steffan]

If anyone is interested, here are some pictures showing how the 2 carbs compare - weather this makes any difference in how they run is questionable.
first picture will the the Fuji: machined base vs bare casting. washers on the butterflies vs not

 

[Aloha Jen]

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[charliemeyer007]

Use a can of WD40 with a pee tube. Quickly and lightly spray the intake manifold mating area while the engine is idling. The rpm's will kick up at the leak. Do the carb base and sections too. Put a big hemostat on the the brake booster hose.

 

[Pighead]

Put a vacuum gauge to your intake manifold and see if you really do have a leak...

 

[steffan]

butterfly pivot - I can't remember for sure but I think they both came long - had to be shortened to clear the vacuum port on the mounting block

 

[steffan]

Use a can of WD40 with a pee tube. Quickly and lightly spray the intake manifold mating area while the engine is idling. The rpm's will kick up at the leak. Do the carb base and sections too. Put a big hemostat on the the brake booster hose.

I had WD40 everywhere - no changes... pulled a strong vacuum. I pulled and blocked all the vacuums lines: brake, PCV, distributor - no change

 

[steffan]

c-clips on the pivots vs spring clips

 

[steffan]

casting differences

 

[steffan]

butterfly finish

 

[steffan]

differences in passageway plugs: brass vs aluminum

 

[steffan]

accelerator pump springs: Fuji has plastic bushings vs not

 

[steffan]

the bolts fixing the two halves together: Fuji is perfectly sized and cleaned vs not so much. Again - makes no difference on performance

 

[steffan]

more castings/ plugs

 

[steffan]

This was one thing I took for granted with the aftermarket carbs. They don't come with any provisions for mounting the throttle cable - Trollhole carbs came with the mounting arm and a cam for correct cable pull. At least for a '72, if you use the standard cable pull, the through will be too long and the pedal will overtravel the carb

 

[steffan]

more plugs

 

[steffan]

Venturi: the fuji ports are a little smoother