Took her for the 1st run today - Backfires a lot while cruising!!

[warthogcrewchief]

Today I got my '89 VR out on the road for the first time since I bought it back in August. I did notice she's a little stiff in the turns (maybe it's me..or the new tires or the fork brace).

 

Anyways, what's getting me is that my bike is really backfiring (frequently) while I'm cruising at around 25-35 mph at approximately 3-4K RPM. She doesn't backfire while accelerating, while decelerating (using either brake or engine/transmission), or while idling.

 

Even though I adjusted the idle knob and throttle cable before riding, she tends to run up to 2K RPM while stopped.

 

I have cleaned out the carbs completely, have replaced the carb intake boots, the carb diaphragm, spark plugs, and doesn't appear to have any exhaust leaks.

 

Any ideas would be greatly appreciated.

[GigaWhiskey]

Just for grins, double check the screws on the diaphram covers. I forgot to tighten a couple in the past.

 

And sneak a look at the boots under the airbox, they like to slip off the carbs.

Edited February 19, 2010 by GigaWhiskey

[warthogcrewchief]

They were tight. I'll try to put fresh gas into it and see if it helps (with a little more Sea Foam).

[GigaWhiskey]

I just added the airbox boots too in the above post.

[BuddyRich]

The first gens are sensitive to any airbox modifications. Check to see that it hasn't had any holes drilled in it and the lid is seating right. What color are your plugs ?

[warthogcrewchief]

No holes drilled in the airbox, airbox boots are seated properly on the carbs. I still need to check the plugs again. I do have the case vent filter mod installed, and the holes in the airbox have been covered with those little rubber nipple covers.

[bongobobny]

Vacuum leak???

[Squidley]

...did you put a carbtune on it also?

[skydoc_17]

If you haven't done a Carb. Sync. yet, that would be the next thing to do. The symptoms you are describing are classic Carb. Sync. problems.

Earl

[Condor]

What Earl said, plus a plug that's only firing occasionally causing the backfiring. These V4's will run pretty good on 3 cylinders.... You might also want to check the vacume bib caps for cracks and air leaks.

[warthogcrewchief]

I know that a few of the vacuum bib caps were old and cracked... I'll change those out when I do a carb sync.

 

So, I guess I'll be getting a carb sync soon as I haven't done so yet.. I've been planning on doing it, just haven't decided which one to buy. I do remember reading the thread about the various carb sync gauges/tools...just gotta decide which one I'm gonna buy.

 

I've never had a bike that performed so poorly just because of a carbs were out of sync. But then again, the V-4 configuration probably has something to do with it.

 

 

Thanks again for the helpful information everyone. I'll report back with the findings when I accomplish both fixes.

[skydoc_17]

Hey Clint,

Kawasaki makes the Vacuum nipples for it's big cruisers and they are over $3.00 cheaper per nipple. As far as a Manometer goes, any of the major brands will be more than adequate for the job. I personally have the Morgan Carb Tune because I travel with my tools regularly and there is no problem with transporting the Carb Tune as it has NO Mercury or a fluid in it. If there is a member close, you might want to invite him over for lunch and a Carb. Sync. (If you lived just a bit closer, I'd be tempted to come there myself!) A Manometer is definitely not a tool that you will use every day, but it is one that you absolutely need any time you adjust or service your Carbs. By the way, do you have ALL FOUR Mixture screws set at 21/2 turns from bottomed?

Earl

[Condor]

Hey Clint,

Kawasaki makes the Vacuum nipples for it's big cruisers and they are over $3.00 cheaper per nipple.

 

Dang Earl, thanks for the lead. Yamaha sure is proud of their's. I'm off to Kawasaki to pick up a few sets for my stash....

[Venturous Randy]

As bob noted, check for a vacuum leak, spraying some starter fluid around the area may show something. Anyone that has a carb sync check that comes up off should check for a vacuum leak before adjusting your carbs to match the leak.

You noted you changed the spark plugs, did you replace the caps? These caps have resistors and can corrode.

One other suggestion would be to unplug each spark plug one at a time and see if you can isolate it to a specific cylinder.

RandyA

[friesman]

Dang Earl, thanks for the lead. Yamaha sure is proud of their's. I'm off to Kawasaki to pick up a few sets for my stash....

 

So another bin is about to be added to the "organizer" in the garage?

 

Brian

[Condor]

So another bin is about to be added to the "organizer" in the garage?

 

Brian

 

Nah... I'm into a new sport. It's called piling....

[warthogcrewchief]

Hey Clint,

Kawasaki makes the Vacuum nipples for it's big cruisers and they are over $3.00 cheaper per nipple. As far as a Manometer goes, any of the major brands will be more than adequate for the job. I personally have the Morgan Carb Tune because I travel with my tools regularly and there is no problem with transporting the Carb Tune as it has NO Mercury or a fluid in it. If there is a member close, you might want to invite him over for lunch and a Carb. Sync. (If you lived just a bit closer, I'd be tempted to come there myself!) A Manometer is definitely not a tool that you will use every day, but it is one that you absolutely need any time you adjust or service your Carbs. By the way, do you have ALL FOUR Mixture screws set at 21/2 turns from bottomed?

Earl

 

I think you're talking about the mixture screws that are underneath the "EPA plug" that gets drilled out? I haven't drilled the plug out on these carbs yet. The only other thought would be the syncro screws on the outboard side of the carbs.

 

Thanks for the info on the vacuum nipples. I'll keep that in mind. I'll see if my local Ace Hardware or auto parts store has them. I have a manometer on order...so I'll have to wait a week or two before it gets here.

Edited February 21, 2010 by warthogcrewchief

[CaptainJoe]

had a 650 vstar that started to occasionally backfire, then, after a week passed it woudn't start at all. I tested the pickup coil and sure enough it was bad as it tested 54 ohms. Was suppose to read 182-222 ohms. GOOD NEWS THEY ARE EASY TO CHECK.

Take your reading on the female side of the electrical clip for the pickup coil (there is two wires going into it grey and black.) My new one tested 199 ohms.

Find the specs for what the specific ohm readings should be for your specific bike/year.

[warthogcrewchief]

I changed the air filter last night. The old one was pretty bad! Since then, the bike is running better. Although I still have an occasional backfire. I plan on syncing the carbs (as soon as my Carbtune gets here!) and also replacing the vacuum port covers for good measure. Hopefully it does the trick....I know I'm headed in the right direction now.... might be tempted to take her for a fast, hard and short 30 mile ride to see if anything clears up.

[Squidley]

might be tempted to take her for a fast, hard and short 30 mile ride to see if anything clears up.

 

No need to ponder it...do it! my '86 I had ran the best it ever did after I basically beat it running 90 mph on the interstate when we were late for a M&E. Bike purred the rest of the day after that

[Condor]

No need to ponder it...do it! my '86 I had ran the best it ever did after I basically beat it running 90 mph on the interstate when we were late for a M&E. Bike purred the rest of the day after that

 

 

Yep, I agree... The '83 never ran better then when I rode her to Ft Collins in '07, and Cody/Yellowstone last year. They just need to get out and stretch their legs to be happy.....

[warthogcrewchief]

I've been riding her to work once or twice last week, and I finally got a chance to take her on a good run. I put about 30 miles on her, about five of it on the highway. She does good in town, decent power... However, on the highway, it struggles to accelerate over 80-85 MPH. It'll hold the speed at 80-85, but nothing much more than that.

 

She still "pops" a little when at idle or coasting, but not big backfires from the exhaust or intake recently. She also tends to want to idle around 2,000 - 2,500 RPM despite resetting the idle screw at 1,000-1,100 RPM before every ride.

 

I'm still waiting for the Carb tune to come in the mail and haven't had a chance to make it to the parts store and get new vacuum plug/covers.

 

Does the lack of power at highway speeds sound like a carb problem or an ignition problem?

 

Thanks for all your help again!

 

WHCC

[Dano]

With the high idle, lack of power over 85 +/-, little popping etc, I'd have to say the carb synch is way off. One of the main indications is the high idle. Make SURE there is some play in the throttle cables, they may be getting too tight (adjustable nut just inside the left lower fairing, follow the throttle cables up). If you have cruise, you can adjust at the throttle grip also. Maybe about a 1/2" twist of the grip should be play.

 

When you do your synch, just remember that all carbs must match the front left (#2) carb. Do the left rear first, then match the right side carbs together then match them to the #2 carb. Probably take you a half hour the first time.

 

Oh, you'll want to make sure you keep the idle around 1000 rpms (right Squid?!) as you're synching the carbs. Thank goodness you're doing a first gen or you'd also need a 5' long screwdriver to do a 2nd gen!

[warthogcrewchief]

Thanks for the tips. I know it's not the throttle cable/linkage. I very familiar with how to adjust the throttle on Yamahas. I adjusted the cable down below until it was just about perfect, and got the top adjustment (just outside the throttle grip) just about perfect too.

 

So, it's gotta be the snyc....boy, I can't wait for this carb tune to come in!

[Condor]

Not getting over 80-85mph sounds like you're running on three cylinders???

On the high idle. Back off the right/left sync screw a bit and see what happens. It may screwed in so much that your idle is actually being controlled by #3 and #4 carbs instead of #2. There's two screws on the right side of the carb assembly. Back the aft one out a bit and see what happens.