Another carb question

[texas-ss-tornado]

Working on an 85, bought non-running. It has a 4 into 1 Holeshot exhaust and factory airbox setup. I took the carbs apart and rebuilt them with a kit, cleaned it all up and put it back together. The previous owner said that he never did anything to the carbs when he put the Holeshot on it, and said it definitely felt like he lost some power, but it still ran OK. I figured while I had them off, I would try jetting them up a bit. I had a set of 155's left over from a Factory Pro kit, and figured what the heck. So I get it all back together and running, idles great, hitting on all 4, sync'd them up without any issue, it just doesn't seem to have the power it should? Exhaust doesn't smell rich, but I'm not sure if the V-Boost is working or not either, I can hear it cycle when I turn the key on, but it also had a T-Boost switch installed and the wiring for it is pretty cobbled together. It runs OK, but it just doesn't pull like it should. I'm just trying to figure out where I should go from here, if I should go back to the stock jets, try some pod filters, maybe I need aftermarket adjustable needles? I'm going to try and sort out the V-Boost before I do anything else, but it's almost like it's not opening at all? What's a good way to actually tell whether it is open or closed? The switch doesn't appear to make any difference in the performance? Any help would be greatly appreciated!

 

[Traumahawk]

Wouldnt the carbs have to be jetted leaner?

From what I know the CV carbs operate the opposite from those on a car. On a car you would jet up because a more free flowing exhaust makes them run lean, but on a bike...it makes the bike run rich.

With slipons you are supposed to jet DOWN one size. From the Vmax dyno day in Topeka ks, I'm running 2 sizes too rich, so I'm going from 152's to 147's.

 

[one2dmax]

Exactly! He needs smaller mains if keeping the stock airbox setup (which makes the best midrange). If you go to pods you need stage seven air correctors. If you go to adjustable needles you also need the smaller mains. If you use our kit and the adjustable needles you need stockish sized mains. If you use our kit and the OEM needles you need larger mains.

 

[texas-ss-tornado]

Wow, I would have thought the exact opposite! I just assumed a performance exhaust would need MORE gas, not less, but that does kinda makes sense now that I think about it. I'd like to use the stock airbox, so I guess I will put the stock main jets back in, what size are they again?

 

[one2dmax]

90 PAJ1
170 PAJ2
37.5 PFJ
152.5 Main

 

[texas-ss-tornado]

Well, now I'm really confused. If stocks are 152.5, why does the Factory Pro kit have 152.5's and 155's in it? What's the point of providing another jet exactly the same size as stock?

 

[Traumahawk]

Wasnt there some years of Vmax...that instead of all 4 jets being 152's....the fronts were 152's and the rears were 150's? Or maybe vice versa?

 

[naughtyG]

Some sizes aren't the same, there's a chart somewhere that shows the size relationship between Mikuni and the ones used in Stage 7 etc

 

[one2dmax]

All years had same size jets front and rear (unless maybe some import version somewhere). Mikuni and Dynojet jets are rated differently so you can't compare by number. I have a chart on our website.

 

[SFCMcGan]

All years had same size jets front and rear (unless maybe some import version somewhere). Mikuni and Dynojet jets are rated differently so you can't compare by number. I have a chart on our website.

According to the 1985 and 1986 parts list.. these models had 150 jets in Carbs 1 & 2.. and 152 in 3 & 4.

 

[one2dmax]

Not that I have seen in personal experience. The only variation I have seen is 100's in the PAJ1 position for the Cali equipped bikes. I think someone said that the Jap restricted version had different jets?

 

[naughtyG]

According to the 1985 and 1986 parts list.. these models had 150 jets in Carbs 1 & 2.. and 152 in 3 & 4.

I remember seeing that in the Yam Service Manual for the early years too, but IRL I always found 152.5 to be fitted on all four..

 

[texas-ss-tornado]

I've got some jets coming from Morley, I'm gonna slap some 150's in there and hope that solves my problem, will update ya'll this weekend!

 

[dannymax]

What needles are in them?

 

[texas-ss-tornado]

What needles are in them?

They look like stockers to me.

 

[dannymax]

They look like stockers to me.

That might account for your power loss, they don't work too well with a aftermarket full system.

 

[texas-ss-tornado]

Well, if the 150's don't do the trick, I've got a set of Factory Pro needles I can swap in there to test, they are set on the 2nd clip from the end if I remember correctly. I sware, I will never understand why guys mess around with these bikes! The factory carb setup was darn near perfect!

 

[Traumahawk]

Well, if the 150's don't do the trick, I've got a set of Factory Pro needles I can swap in there to test, they are set on the 2nd clip from the end if I remember correctly. I sware, I will never understand why guys mess around with these bikes! The factory carb setup was darn near perfect!

LOL...face it...its never enough. We want MORE....more power, better ride, more cornering ability, thats why we love these bikes....they are a GREAT platform to start with...(atleast thats what my monkey tells me....lol)

 

[texas-ss-tornado]

Well, I put the 150's in today. Good grief, what an ordeal. First of all, somebody needs to explain to me HOW you can change the main jets out without taking the float bowls off. I took the carbs off and attempted the first one with them still attached to the bike. First attempt to break the jet loose and the slot in it disintegrated like the dead sea scrolls! I could not believe it! So I had to take them completely apart anyway, off the bike, and even OFF THE BIKE, I could not get the other jets out WITHOUT taking the float bowls off! It's impossible! They do not come up far enough into the hole to come out, they just fall into the float bowl area! What a joke. I was so friggin' pissed! One thing after another with these carbs, one of the float bowl screws wouldn't come loose, and I just had these carbs apart a few weeks ago! Had to get my dremel out and make a long cut through it and get it off with a flat head screwdriver. Then once on the bike, my choke mechanism came apart, the clip on the back fell off and went to God knows where. Oh, and when I went to put the carbs back in, I couldn't find the hose clamp for the main fuel line? Looked all over? Guess where it was? Fell into one of the cylinders, sitting down there right by the open valve! Was able to snake a coat hanger down there to get it out. It was just a comedy of errors, nothing was going right! I finally got them all put back together and running, no leaks, runs BETTER! Still not like most of the STOCK VMAX's I'm use to, but better than before. I have SOME top end rush now, but still not enough. I'm also hearing a few "PPPFFTTs" at low RPM coming from the airbox. It's a stock airbox and filter. The only other things I can do now are try pods or maybe even try the Factory Pro needles. I'm making progress, but slowly!!!!!

 

[Traumahawk]

I'm glad that its better than it was!!