Surging at 3k-4.5k RPM

[Bts-gtx]

Hi all, I've read a number of threads and just wanted some more input. 1988 1100 with a Vance and Hines pipe, stock air box, K&N filter. It seems to surge around highway speeds, 3k-4.5k RPM. The other threads suggest it's possibly the float height(lean condition) or carb sync. Any other ideas or areas I should tackle first before I look into the carbs?

Mid range is handled generally by the needles, right? Would it be worth lowering the clip on them? The plugs look fine (nice tan color).

I'm hoping someone has a quick fix to get me through the summer and I'll do the carbs this winter...hoping....

Thanks,

[Hoevding]

Probably your engine is to lean. You said you have K&N filter, or filters? If you have replaced your standard filter with ONE K&N its probably the same as stock, but if you have K&N sport-filters (one per carb) it will lean out your fuel/air mix. This should be possible to "read" on the condition of your sparkplugs. A good indicator of lean fuelmix is If the engine has to be run on choke for a long time. If my thinking is right a set of bigger mainjets may solve your problems, i donīt think changing the float hight is recommended. A carb sync is good anyway, if its a long time since the last. But also have in mind that aftermarked, or performance hardware as exhaust-systems, air filters, and so on donīt always match the factory set up. Remember that most bikes are produced as a compromise for the average user. If you want to win power in the top end, you have to sacrefice in the low or middle range. As a good rule; if you change something on the exhaust side, you have to change something similar on the inlet side, and vice verca.

[Bts-gtx]

Thanks for the info, K&N is a single with stock air box.

[Hoevding]

Some of those aftermarked filters have to be oiled in. Check with the manufacturer if your filter have that feature

[DClark]

Hi all, I've read a number of threads and just wanted some more input. 1988 1100 with a Vance and Hines pipe, stock air box, K&N filter. It seems to surge around highway speeds, 3k-4.5k RPM.

Thanks,

That range is where the carb needles come into play. The problem is the filter. It isn't just that it is getting too much air and that makes things lean; it is that the there is less vacuum created by the K&N.
The needles need vacuum to be raised (which allows more fuel to flow). If you have insufficient vacuum, they won't raise as high as they should and bike will run lean.
Now, the obvious could be suggested- raise the needles. Well, that can help, but it won't cure it. From my own experience, for some reason, the idle was not as smooth with K&N as it was with oem filter.
I have a FP jet kit, kerker 4-1 and went from K&N back to oem and what I noticed was a little less wot, but better idle and better tractability. The driveability is so much better than I am sticking with oem. Oh, by oem, I mean Suzuki brand filter, not an emgo or other aftermarket one.

[Bts-gtx]

Thanks gentlemen, the filter just might be the culprit. It makes sense considering the carbs are vacuum slide. I'll try adjusting the needle height, it that doesn't work I'll go back to the stock filter. Hopefully that helps. If not it looks like I'll pull the carbs in the winter and see if there is something obvious there.

Any issue with running this over the summer if it's not the filter? A little lean shouldn't harm anything, right?

[DClark]

One more thing- you didn't say what jet kit you have.A piped bike needs one and the kits out there are dynojet and Factory Pro. If it is dynojet, you'll need to throw it in the trash and get a FP kit, new springs and possibly new pilot air jets. it is impossible to dial them in,
If you have the kn and want to put off making it run right, raise the needles one notch and keep your kn filter. Somewhere on this sight, I did a comparo between both kits.