Rejetting Help

It is winter and way to cold to ride here in PA so I dissassembled my SV-650 so i could clean it up and eliminate the huge tail section, install my vance and hines full exhaust, desnorkel the intake, and rejet. I am having a hard time deciding on what main jet size to use, and I really dont want the bike to run crappy. If anyone has any recommendations i would really appreciate it. I have read John"s SV650 pages in which he talks about using 152.5 on almost the same setup as me.

Also my dealer is able to get me "suzuki" jets and not the ones recomended by John on his web page. Are different brand jets sized any differently than others.

2000 SV 650
Vance & Hines S4 Full Exhaust
Desnorkeled Filter
May possibly raise tank.

My advice is to use a previously proven formula. Unless, that is, you plan on spending some time on the dyno. If you can get hold of some settings to use as a baseline, that'd be a good place to start. Then you could go and make minor changes is need be. You mentioned using 152.5 mains. What are the other figures for that set up (ie pilot, fuel screw, )?

Why not more than 20,000 in the poll?


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[johnnyrod]

My best advice, don't bother desnorkelling, just get a decent air filter like BMC or K&N. You really need it set up on a dyno cos jets from different sources with the same nnumbers on them give different fuel flows. This is really only the tip of the iceberg, talk to a dyno shop first for some info, this bit is free.

[mattSV]

IIRC different companies use different different ways of measuring - therefore, a 152 dynojet might be different from a 152 suzuki part

Also, I think that set ups for the States would need to be a bit different (different humidity/fuel quality etc) - investing some time with a dyno tuner would probably be well worth it.

[northwind]

I'm not sure about how the desnorkel works out as compared to other filters, but I suspect that 152.5 DJs is a good size. It'll certainly be better than stock... You'll need to adjust the idle screws and if it's a US bike, use shims to adjust the needle height as well.

"Suzuki" jets will be Mikuni I suspect, since they build the carbs for the SV IIRC. Mikuni use a different measuring system based on flow instead of size (or size instead of flow) which usually means their jets are around 5-10 sizes bigger than the DJs that most people use. (my Mik 140s are roughly equivalent to 146/148 s far as I can tell)

I'm just at the end of much the same process as you, and I'd recommend you get it to a dyno for fine-tuning anyway... You can probably get it 4/5, 9/10 of the way there by butt dyno but if you're paying out for a full exhaust I don't see the point in trying to economise on setting it up. Plus lean running doesn't just leave you running badly, it can damage your engine over time.

So what I'm doing is getting it as close as I can to cut down on dyno time, then I'll take it in for finishing. For the record, I'm running a BMC Race RS filter (best flowing standard-type filter for the SV), Chewy's tank spacers, full WRP race system (well, usually I am) and a DJ kit... 2 3/4 turns on the idle screws, 3rd clip on the DJ needle (if you're using stock US bike parts, you'll need to use wee shims instead) and 160 mains. Still a little lean at WOT and a bit lumpy at idle though

Wow thanks for the replies, of course i will be adjusting the air-fuel screw probably 2.5 turns out, and two shims on the needle. I am going to get 17.5 pilot jet size i think, (depending on which jet manufacturer).

Hey northwind what do you mean DJs? or DJ Kit? and how do you know it is alittle lean at wide open?

I did put out the $$$ for the exhaust but to be honest i can't afford anything else, (ie. dyno time.)

I dont care too much about making the most power from this bike, i just want it to run right and sound good. I dont want to foul plugs or screw up the motor.

The reason for not more than 20,000 on the poll is because all the bikes around here seem to have alot less (around 5-10K). Mine has 17,000

So the setup i heard about and was dyno'd by someone was
152.5 Mains
17.5 Pilots
Two Shims on Needle
Drilled Slide Hole
Desnorkeled Filter
2.5 Turns out on air\fuel screw
Vance and Hines S4 Full system

I am mechanically capable, but have never worked on bikes or carbs, anything i should know???

Any better places to get jets?

[northwind]

Sorry, DJ was just an abbreviation for dynojet, they make kits but also sell jets individually. If you buy the normal dynojet kit, BTW, the jets don't go high enough IMHO, the biggest is I think 148.

DJ are the most common jets, I think- they make the most common kits, and the dyno machines for that matter So when people talk about 150 mains they'll usually mean dynojet.

We get bigger pilot jets to start with on the UK bikes, forgot about that.

I'm kind of assuming mine's lean at wide open... i have the classic SV bump at 5/6000 revs that tells you you need bigger mains (if you cruise at 5000-6000 then crack the throttle open, it lurches and is slow to respond for a moment, then picks up) It's gone with the twin system it's been wearing for the last month, but still happens with the single.

The only thing you really need to know, is that the screws in the carbs are absolute crap and can be difficult to get out. I would invest in a pair of good mole grips and an impact driver (screwdriver you work by hitting with a hammer) before you start, because they're tricky to get apart. I've got the spec for the screws somewhere, I'd try and have better replacements with a hex or allen head to hand as well... Chances are you're going to mangle at least one screw beyond reuse.

Remove the choke cables from the handlebar end if the screws at the carb end won't shift- great tip I got from Viney. Saved me a lot of hassle.

Other than that they're dead easy to work on. Just badly specced screws as usual.

[johnnyrod]

The midrange dip could be a fuelling problem, and this is the sort of thing you pay the dyno time to get rid of, or it could be if you have a noisy can on stock pipes, as it comes down to the pipe sizes and lengths etc. and won't go away until you replace them too.

You shouldn't need to alter the pilot jet etc. just by adding a new exhaust, it would really take much more modification than this to need to rejet the pilot circuit. As for the mains etc. it is impossible to say, as MattSV says the air conditions etc. are different as well. As for drilling the carb slides, you might find they lift too fast for the set-up you have, so instead of a snappier response you'll get a bigger lean bit before it starts going again.

It's impossible to get CV carbs right by fiddling and riding, I'm not trying to be a pain in the **** but there are a lot of variables to take into account. If you really can't afford dyno time till this time next year (say) then I'd suggest go up one size on the main jets (same jet manufacturer, don't worry about using Dynojets or it'll just get confusing), maybe and extra 1/2 turn of pilot screw (rough running on choke at idle means you've overdone it), and if it really is crap in the midrange then add one shim under the carb needles.

[northwind]

Originally Posted by johnnyrod

The midrange dip could be a fuelling problem, and this is the sort of thing you pay the dyno time to get rid of, or it could be if you have a noisy can on stock pipes, as it comes down to the pipe sizes and lengths etc. and won't go away until you replace them too.

That was me that had that not the guy who posted the thread... I know exactly how to get rid of it, just don't want to try and get the carbs off while on crutches I've been running with 2 different full systems and various filters so I've not got everything how I want it yet

You can't get perfect setup without a dyno but you can get a pretty good result if you're prepared to fiddle and you can diagnose the shortcomings accurately... Certainly good enough to get good running and avoid going dangerously lean or fouling plugs. But you're certainly right that dyno time is hte only way to get it perfect.

If I didn't enjoy tinkering so much I'd've had it on the dyno the same day that I changed the exhaust, the extra cost balanced agaisnt the time and effort to change the settings myself would have balanced out I reckon...