23 Vanguard Random Momentary Power Loss

[slonomo]

Originally Posted by flyby71

Here is the carb that’s on it now.

Yep, stock Briggs 2 barrel.

If you are into switching carbs, I purchased a kit from a place called Backwater Performance. The kit comes with a manifold, gaskets, and a Mikuni VM34 34mm carb. The kit is made for a mudboat, but you can order it without the boat throttle and rev limiter, that's what I did. You also can use the kit for the Predator 670 as the manifolds are the same bolt pattern. I also tried this with a 44mm Mikuni CV carb from a Yamaha Grizzly 660 atv. Both ran really well, the larger carb had crazy power in the higher rpm ranges, but it would flood the right side cylinder at idle, probably from a fat idle circuit jet. I lost patience and got the 34mm kit. That one ran fantastic and was more tame, idled quietly at 900 rpm and had excellent throttle response and feel.

[flyby71]

Originally Posted by slonomo

Yep, stock Briggs 2 barrel.

If you are into switching carbs, I purchased a kit from a place called Backwater Performance. The kit comes with a manifold, gaskets, and a Mikuni VM34 34mm carb. The kit is made for a mudboat, but you can order it without the boat throttle and rev limiter, that's what I did. You also can use the kit for the Predator 670 as the manifolds are the same bolt pattern. I also tried this with a 44mm Mikuni CV carb from a Yamaha Grizzly 660 atv. Both ran really well, the larger carb had crazy power in the higher rpm ranges, but it would flood the right side cylinder at idle, probably from a fat idle circuit jet. I lost patience and got the 34mm kit. That one ran fantastic and was more tame, idled quietly at 900 rpm and had excellent throttle response and feel.

Hey Slo, I just read a thread where you said that you thought the 34mm was too big for a 23 vanguard and that it doesn’t do well at lower RPMs. The cut out from the stock carb is getting more and more noticeable, so I’d like to do something. Would you recommend playing with the stock carb and hoping that it can get to working better, going with the 34mm from blackwater, or do you have another option that you found optimal?

[slonomo]

Originally Posted by flyby71

Hey Slo, I just read a thread where you said that you thought the 34mm was too big for a 23 vanguard and that it doesn’t do well at lower RPMs. The cut out from the stock carb is getting more and more noticeable, so I’d like to do something. Would you recommend playing with the stock carb and hoping that it can get to working better, going with the 34mm from blackwater, or do you have another option that you found optimal?

Well, the 34mm was worlds better than the stock 2 barrel in overall throttle response, power, and idle quality. With that said, a 32mm would be better for lower rpm use IMO. Either way, a proper throttle cable setup and jetting is key. The conversion is NOT a simple bolt it on and go, it will take a little work and persistence to get it right. Some would say it's too much work, but for me it was the right choice.

If you're not into fiddling with a carb then I'd keep the stock carb and make it work, or get a newer/different stock carb. If you like a challenge and classify yourself as a motorhead/backyard mechanic then you would do just fine. I had to read quite a bit about tuning the Mikuni's to fully understand what is actually going on and how to get it right. It's an art.

[flyby71]

Originally Posted by slonomo

Well, the 34mm was worlds better than the stock 2 barrel in overall throttle response, power, and idle quality. With that said, a 32mm would be better for lower rpm use IMO. Either way, a proper throttle cable setup and jetting is key. The conversion is NOT a simple bolt it on and go, it will take a little work and persistence to get it right. Some would say it's too much work, but for me it was the right choice.

If you're not into fiddling with a carb then I'd keep the stock carb and make it work, or get a newer/different stock carb. If you like a challenge and classify yourself as a motorhead/backyard mechanic then you would do just fine. I had to read quite a bit about tuning the Mikuni's to fully understand what is actually going on and how to get it right. It's an art.

If you went with the 32mm Mikuni, would you use the Backwater adapter or the Performance670 adapter (I’m assuming they would both fit the 32mm and the 23 vanny)?

[slonomo]

I think either one would work the same. I used both. First I used the Perf 670 version, much cheaper, but had some flooding issues at idle. I thought it was the 670 carb intake, but it turned out to be jetting. The same carb flooded with the Backwater intake. So either one. But again, jetting is key. It turned out the pilot jet was too fat, Vanguards like very little fuel at idle. The stock carb has trouble idling at 1200 and below. The Mikuni will idle at 800-900 rpm, but you have to get the mixture just right, on the lean side at idle.