carb jet query

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02GF74

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Firstly have 1998 Vmax full power imported from Japan. The carbs needed cleaning, which was done, but I made two mistakes.

a. I did not make a note what jets were fitted, in particular main and pilot.

b. I ordered 4 rebuild kits, off eBay from China, and the old adage "Buy cheap, buy twice" springs to mind.

One of the kits is missing the gasket and 2 rubber bungs, not the end of the world but the pilot jets are unmarked and all look the same; I inserted a sharpened wire and seems the holes are same diameter. The main jets are GL87 x 8, GL94 x 3 and 1 unmarked, so not four sets of 3.

The kit should contain main jets in 3 sizes: 150/152.5/155 and pilot jet is also 3 pieces:37.5/40/42.5.

To be fair, the cost of the kit from China is about the cost of 2 main jets from UK so I suppose for the parts that can be used it is not money totally wasted.

Anyway, to get myself out of this hole, I'm going to need some help.
1. What jets should be fitted?
Manual lists European and US, which is neither:
Vmax carb :Mikuni BDS35
Main jet European: 150 US 152.5
Pilot Air jet 1: European 95 US. 90
Pilot jet European 42.5 US. 37.5

I may be able to buy the main jets separately, so should I get US or European? (I think the only way is to take the carbs off again ARRGGGGHHHH - or buy both sets). In theory I should not need to after being cleaned but just in case.

2. What effect does would fitting 152.5 instead of 150? And vice versa?

3. What is meaning of main jet GL87 and GL92

4. I've located source of Mikuni jets, which look like they are correct but only have dimensions as below, are these correct for Vmax carb?

5. What effect would fitting 42.5 instead of 37.5 have, and vice versa

Thanks in advance.
 

Fire-medic

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Sean Morley and dannymax will both tell you the same thing, "buy OEM parts!" Especially for important precision things like carburetor jets.

That said, I've had good luck with K&L parts for carb kits. I do buy OEM jets, better quality control. I've read where people had your exact issue, they bought cheap kits and installed the parts only to end-up with crappy-running bikes, because the jets were inconsistent in sizing, though they were marked the same. "How can it be the new jets that are causing my problem, they're new!" That's why it's a good idea to replace one thing at a time, so you know what piece did what effect. I'm not-saying, replace your main jets one at a time, and re-install the carbs, and try running it, in-between main jet (or pilot jets) replacements. Going from a stock exhaust to a Kerker or UFO 4/1, and not installing Sean Morley's jet kit and modified air filter lid, or a Dynojet Stage 7 (Not a Stage 1 Dynojet, run-away!) carb kit, and not-spending the time to tune it will just give you a crappy-running unsafe bike you will want to burn to the ground.

I'll tell you my thoughts:
Since you're probably not at 5,000 ft above sea level, your bike probably could stand a bit of leaning-out. I would try Mikuni main jets, 147.5, and 37.5 pilots. Of course, when working on your carbs, re-synch them once they've been removed and worked-upon, and re-mounted.

Be sure to check your dry float level setting, while the carbs are off and apart.

VMax FloatLevel bowl off.jpg

Mikuni larger # = larger holes, i.e., more-gasoline.

The bikes come rich from Yamaha, less-chance of doing damage to the bike that way. Of course, you're probably not gonna be holding the throttle wide-open for 5 minutes anytime.

The O.A. jet dimensions you show are roughly the correct measurements for a main jet.
 
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02GF74

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Sean Morley and dannymax will both tell you the same thing, "buy OEM parts!" Especially for important precision things like carburetor jets.
I appreciate what you are saying but the Vmax was made to satisfy the US drag strip culture and only arrived in UK in 1991, full power available from 1996. Therefore there are fewer on the road and few parts suppliers. Ordering from US becomes costly due to postage, then getting stung by the Post Office for import duties.

I was in Austin, TXs for 6 months as well as spells West Greenwich, RI and going round the shops, just about every item has "Made in China" tag so there should be no reason these carb kits are inferior in any way. I bought the kits in anticipation I would need to replace parts but I managed to clean the jets as well as being able to re-use the gasket, the only damage was corrosion to the two screws holding the jet block - even if the rest of the kit is garbage, it is still just about worth it the screws. Most annoying is I did not note the jet numbers.

I know someone is about to pipe saying thou must not re-use gaskets- these were completely undamaged and I see no reason why they won't seal.
 

Traumahawk

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As long as the Bike is full power the only difference in the jets is due to emissions is my understanding. Now that being said, a change in a jet in one area, makes you have to change other areas as well.

The MK 152.5 main jet is actually a little bit rich. The bike should run better with the 150's. I would use the 37.5s on the pilot jets. Pilot jets affect 0-to about 4000 rpm, and about 1/8th of the throttle. Standard setting on the screws for the pilot jets is about 2.5 turns out. If you use a bigger pilot jet, then the amount of turns out on the screws would be less.

PAJ#1's affect the amount of air coming into the carb circuits at idle. Regular US was 90, and california models used 100. (so more air at idle ONLY......again, an emissions thing)
PAJ#2 (behind the diaphragms on the side of the carbs under the covers), control the amount of air going into the circuits just off idle all the way thru redline. Stock US was 170's.

Hope this helps.
 

Fire-medic

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You should be able to find Mikuni jets in the UK, try a shop doing performance work, or vintage racing, they will be able to get them. You can go with the aftermarket stuff, as I said, I've had good luck with K & L. Other than that, I'm not-familiar what aftermarket suppliers there are there. A bit of time on the internet should get you contact info/locations of UK Mikuni distributors/dealers. As-to the quality-control of Chinese parts, it's been a topic of concern in the bike magazines where they are doing mechanics problems. Call Allen Millyard, and ask him what he thinks of precision Chinese parts. Yes, I'm sure there are many good suppliers where the parts are 'made in China,' but there has been enough concern with the stinkers, too, for me to-mention it. Why can't they label the jets with common sizing labels, instead of what you found?

Try these guys:
http://www.allensperformance.co.uk/
Your sole UK distributor for:
Mikuni (Aftermarket) carburettors (Including VM, TM, TMX, RS, TMR, TDMR, HSR)


Keihin (Aftermarket) carburettors (Including PJ, PWK, PWM, CR, FCR 28-41mm)

We can now also offer a range of parts for Mikuni OEM carbs

http://www.motocarb.com/
New genuine Mikuni motorcycle carburettors and spare parts:
" we stock a full range of calibrated tuning parts, main jets, pilot and air jets, needles, needle jets, throttle valves etc."
 
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