Hello again, you may remember me with the fuel problem....

http://www.vn750.com/forum/showthread.php?t=2325

To continue the quest for a better performing bike, I need to know what others have experienced with their vacuum guage.

Mine will wildly swing at idle but will smooth out as throttle is increased.

I syncronized the carbs today and they will sync at 4000 rpm but at idle the rear cylinder has a lot higher vacuum than the front.

I am using Marty's yard stick manometer

http://www.powerchutes.com/manometer.asp

any sugestions? I know from a vacuum check on my car, that the needle should be steady at idle, otherwise you have a vacuum leak or the carbs are too rich or too lean. Which is it for these bikes? Do I need to enrichen the jets? (Oh yeah, I forgot to tell you I only have one vacuum line from the front carb, all the others are gone, and I replaced that hose so probably not a leak.....will the idle adjust effect the sync?

The bike seems to run ..OK, not super, but ok. Maybe I am too pickey and expect this 2 cylinder to run like my '71 honda 750 4cyl.

Thanks for any assistance you can provide.

I will be ear shaving in the very near future and need access to a set of jets and shims, I have tried the links in the verses, but none acctually tell me which jets and shimms are for the VN750.....

Thanks again.

I guess everyone elses' vacuum is fine....

I have never checked mine so i cant help

I have never checked mine so i cant help
Ditto

Maybe I will have to repost during the week....

Thanks

Me either. Although some people say that the vaccum between my ears is good. I don't know how they know my bike has ears...

When the bike is at idle "I think 1100 RPM" you will need to restrict the tube to get a steady reading. Most carb sync. tools come with little wire restricters. If yours doesn't you will need to find a way to pinch off the tube a bit. Sometimes a small pair of loccking pliers or small c-clamps. Hope this helps!

tinocker, can you please explain in as much detail as you can, I cannot find any info on this. I can see restriction, but I cannot see how it will help with on side having more vacuum than the other at idle....There needs to be some way to adjust each side????

Thanks.

I'm having the same rpm swing at idle - dta116, did you ever find a solution to your problem with the same?
Thanks.

There needs to be some way to adjust each side????
If you need to set the carbs so one matches (or is in-sync with) the other, I don't see why you'd need to be able to adjust both.
Just adjust the one 'til it is the same (or very nearly the same) as the other.
Or am I missing something else here?
All I could find on a search were instrucions which say "Adjust the dampening valve to reduce the studder of the needle, or mercury"
There were no pictures to go along with it.

All the carb sync stuff basically says to go with the one screw - between the carbs - and try to even up the pressure (with the screw adjusting the vacuum in the rear carb). But will out o' sync carbs affect the rpms at idle? "Dampening valve" would seem to be some other beast...

Maybe I'll go to the Kihen (Kiehn?) link and see if they have any better pics.

"Dampening valve" would seem to be some other beast...

Sorry Cindy, that was for where dta116 was asking about the 'restrictor' that tinocker had mentioned.

I wouldn't think being out of sync would effect rpms @ idle too much, but, not having done a carb sync, I don't know for sure.

Okay. That makes more sense now.

dta -- are you out there? When you sync'd, did your rpms smooth out???

I have been making numerous mods since I first posted, Still not sure it is not normal for the fluctuations at idle, I did sync the cards at idle and checked the vacuum while increasing the throttle and it only takes very little throttle to smooth the needle. It may be that two cylinders may be on the edge for standard vacuum gauges to perform steadily.

The bike is running flawlessly, and much more powerful after the carb work and tune ups of all things "Bike".

Just completed an "Ear Shave" with K&N's and it will be a while before I complete the proper jetting. Still studying all the idiosyncracies of this "magic" art of jetting.

Anyway, after syncing the carbs at idle the vacuum gauge is still the same, but I'm almost sure everyone should have the same results.

I will keep the forum up to date.

Thanks for the update. I did a "by ear" sync of the carbs over the weekend, and it runs more smoothly, but I'm still not sure about the idle rpms. Plan to take the bike out for a longer ride this evening, so I'll have a better sense of what I've done for it...or to it.

BTW, when you did the carb sync...can you tell me how you hooked up the fuel lines? There's a Verse that talks about using a T link from the petcock, etc., but I'm not totally understanding what I need to do to ensure that there's fuel flowing. Got the $2.00 manometer all set up - just need to finish understanding the process.

Any help you can provide from your experience would be greatly appreciated!!

Thanks.

Cindy,

The T fitting is used because the left carb supplies the vacuum to the petcock. The vacuum is what allows fuel to flow thru the petcock to the carbs so that we don't have to turn the thing off everytime we shutdown the bike. It helps prevent flooding. The T fitting allows you to hook up the manometer while keeping the vacuum to the petcock.
If you look at the petcock you will see three lines leading to it. 2 are fuel feeds, one main and one reserve, the smaller third line that hooks to the vacuum port on the carb is the one that supplies the vacuum to the petcock. This is the line that needs the T fitting unless you are lucky enough to get your carbs sync'd before you run the gas out of the float bowl. I believe you may get erroneous readings though as the fuel level decreases.
I'll try and shoot some pictures in the near future as I will have to pull the carbs on Ursula and clean them out. Seafoam is no longer working. I'll resync on reinstall and document the procedure here.
Hope this helps for now.

Cindy,

The T fitting is used because the left carb supplies the vacuum to the petcock. The vacuum is what allows fuel to flow thru the petcock to the carbs so that we don't have to turn the thing off everytime we shutdown the bike. It helps prevent flooding. The T fitting allows you to hook up the manometer while keeping the vacuum to the petcock.
If you look at the petcock you will see three lines leading to it. 2 are fuel feeds, one main and one reserve, the smaller third line that hooks to the vacuum port on the carb is the one that supplies the vacuum to the petcock. This is the line that needs the T fitting unless you are lucky enough to get your carbs sync'd before you run the gas out of the float bowl. I believe you may get erroneous readings though as the fuel level decreases.
I'll try and shoot some pictures in the near future as I will have to pull the carbs on Ursula and clean them out. Seafoam is no longer working. I'll resync on reinstall and document the procedure here.
Hope this helps for now.


Thank you, thank you, thank you! That helps a ton - and if you have pics of how you hooked it up, that'd be awesome. I'm bound and determined to do this myself, but just want to make sure that I'm not missing any critical steps along the way.

Thanks again!!

Im just joining this thread to watch for the photos. I'm going to sync mine soon. Thanks!

Quick question about the t-fitting: my partner used to be a veterinary nurse, and said that they used manometer-type deals all the time to check....hmmm...lung pressure in horses? Anyway, she said that the t-fitting has a valve so that the flow can be closed or open, depending upon what one is trying to do.

So I'm thinking: close the valve so that it's just a vacuum check while reading the manometer; then open the valve (as the fuel gets a little lower) to let some more fuel into the carbs; then close it again to run the vacuum check. Is that about right?

Also - what size t-fitting? 1/8" ID?

Thanks!

BTW, I took my baby into town last night, and my "ear sync" was a disaster. Apparently I am tone-deaf - poor thing ran like I'd bought it sight-unseen off of eBay.:doh:

Cindy, I was wondering about that. I've sync'd both my kz's with 4 cyl and I don't think I could "hear" it sync. It was purely visual. I'm sure it's different on a 2 cyl engine, but still I'd think you need the meters. I've got to give you credit for trying it though! I probably wouldn't have tried that, just too chicken.

I'll bet once one of these 2 cyl v-twins are sync'd, it will feel a lot better on the road.

Well as my mechanic buddy said, "When it stops running altogether, you know you turned soemthing too far." So I took that as my lead.

I made my manometer this weekend (need to pull about 4 inches of oil out - it's a little high), so now I just need the t-fitting to finish the job. I agree that visual has got to make more sense, at least until I can see/hear what I'm doing.

And quite for certain - almost anything I do to it at this point (short of the bike not running at all) - will be an improvement over my last 'fix.' :smiley_th

Cindy, You can sync the carbs with the tank on...just find a "tee" for the left vacuum line and direct to the carb on the right side.

start it up and watch the level on one side go way up. Go slow, adjust very little and watch, then a little more and watch, soon they will be even, that is where you stop. You only adjust the sync for idle, but I am curious if yours changes significantly if you crack the throttle a bit.

By the way....the idle will change a little, try to keep it adjusted around 1100-1200.

after you sync, then readjust the idle richener screws for the highest idle on each side.

Oh yea...If you did an ear shave without rejetting, you bike will run like crap...I know, thats where I am right now...I will be spending the weekend with jets in hand.....

Someone said you can rejet without pulling the carbs, but I have my doubts.

Dave

I've still got my ears, so I'm okay in that respect. ;)


But I'll definitely take it slowly on the syncing. And I was thinking that the sync is at idle, so some of the other posts about "performance at 4000 rpm and up" had me confused.

Question, though: I finally drilled through the lead plugs on my f/a adjuster screws; should I set those back at the factory setting (1 5/8), set the idle at 1100 using the idle adjust knob, and THEN sync? Or should I get the idle set at 1100 - turning out the f/a screws for a less lean flow - and sync after that?

It may not matter, but in case it does, I just want to make sure I'm not doing things out of sequence and thereby causing problems down the pike.

Cindy, I don't think it matters, as long as the bike is idling pretty good.

I sure wish someone would post some photos of syncing with the tank on..anyone? When I get around to doing this, I'll certainly shoot some photos and do another writeup on my website.

Alright, I went out and bought a t-fitting (1/4", per someone's instructions), and darn it if it didn't fit anything at all. Nothing. However, since my manometer had evened itself out overnight and was sitting perfectly at 27", I decided I'd try to sync the carbs without the fitting. Here's what I did:

Started up the bike on reserve, then shut it down. Pulled the vac hoses off of both carbs, and hooked up the manometer hoses (dang they're hard to jam on there!). Turned on the bike and took note of an *obvious* difference in vacuum, with the frontcarb doing most of the pulling. Shut it down, opened the throttle so I could reach the adjusting screw, turned the screw to the right (to increase the vac in the rear carb). Turned the engine back on, and had overadjusted and now the rear carb was doing all the pulling. Shut 'er down, and adjusted back towards the middle of the two spots (kinda like shooting cannon balls - aim high, aim low, aim for the mean). Futzed around for a bit, and then ran out of fuel in the float bowl.

Soooo, unhooked the manometer hoses, hooked the vac hoses back up, turned the bike on again (using reserve - I was thinking that might just put a little more sumpin' in the float bowl), ran it about 30 secs, then turned it off. Hooked the manometer hoses back up, and continued to fiddle with the adjusting screw until I ran out of fuel again.

Repeated the above sequence (it gets easier by the third try), and then fine-tuned the adjustment with the remaining fuel in the bowl. I ran it for another 15 secs or so, and it was nearly dead-on even up. Sync'd!! :pepper: And it probably took no more than about 25 minutes, even with the false starts with the t-link. :notworthy

Unhooked the manometer hoses, rehooked the vac hoses, made sure the connections were tight and the clamps were solidly in place, and then took the bike out for a few miles. Smoooooooth! It was very nice! :smiley_th What was interesting, too, was that I had to adjust how I was opening the throttle - I think the carbs were so out of sync previously that one carb (probably the front) was kicking in earlier than it should have if the throttle had been adjusted properly. Once I realized that tonight, I was more careful in the clutch-throttle action, and the bike ran like a champ. One little backfire from the right pipe (need to enrich the mixture on the right side now), but the decel popping is mostly gone, and the stumbling engine similar smooth.


THANKS to everyone on this site who's offered advice and suggestions - or even just encouragement to take on these little projects. They're eminently do-able with a few tools and a lot of patience - and it feels a whole lot better having a fine-running machine and my money still in the bank!!

Well, Cindy, you're my hero. After reading this, I may be able to do it myself.

Great job! Can't wait to try it myself! X2 on the hero thing!

I knew you could do it!!!!:motorcycl

Way to go Cindy!! http://www.addis-welt.de/smilie/smilie/schild/icone14.gifhttp://www.addis-welt.de/smilie/smilie/schild/You_Rock_Emoticon.gif

Thanks, Guys!

I think my work for the week is done. Wonder if they'll let me leave my day job until next Monday? :D

Seriously, though, "there is no 'i' in 'team'" - if it weren't for the Forum, I'd have never tried to do any of these adjustments to the bike. This is a great group!! :rockon:

To: Cindy's Boss

Cindy will not be coming to work for the rest of the week.
We here at VN750.com have all got together and decided she deserves a break from the everyday grind.
She needs to relieve the stresses put on her, while at work, by enjoying an entire weekend of Vulcan Cruising !
We are sorry if this is any inconvenience to you or the company, but you've brought this on yourself.
If there is anything we can do for you, please leave a post at VN750.com. We will do our best to help you out, as long as it has to do with Vulcan 750 motorcycles.
In closing, please keep in mind that because Cindy is now a member of our group, she has the right to A) Either leave work early when weather is better suited for riding rather than working, or B) Just not coming in at all so she can sit in the garage and look at her Vulcan, during bad weather condition, and imagine she's out cruising.

Thank you for your understanding in this matter.


Sincerely,
The VN750 Gang

Way to Go CINDY!!!!I will happily co-sign the letter Hyper!

I am lucky enough to have a m/c shop who will help me FOC (free of charge) and whose tools I am allowed to use, but I will not hesitate to let you folks help me out when I need it. This site ROCKS!

kait

(Oh yeah, I forgot to tell you I only have one vacuum line from the front carb, all the others are gone, and I replaced that hose so probably not a leak

is the vacuum nipple on the rear carb blocked off? it should be connected to the front one with a 'T' piece, then to the petrol Tap, but if its not used, try blocking it with a small piece of hose with a bolt in, both vacuum readings should now be equal ;)