Hesitation/Miss when it's windy

[dbthomas]

First post. I purchased a 1994 Vmax with 11.6k miles last summer from a friend. He bought the bike to flip. It had been sitting for several years. He had the carbs professionally cleaned by a trusted mechanic. He sold it to me with full disclosure that it had a miss (also no front brake so i wasn't able to get a feel for the miss until I fixed that). He thought the problem might be a coil going bad.

Once I took it on some rides I discovered it would run great for first several minutes, but there would be a slight hesitation once it was fully warmed up if I gunned it at around 55 mph. I purchased some GSXR COPs, custom wiring harness, and new plugs. I installed the rear COPs first (easiest) and took it for a ride. The same symptoms existed. But this time I decided to give it a little choke because it felt very similar to a lean condition. The problem went away. I turned the choke off, and it still ran great. No hesitation. I rode it for a couple more weeks and could not get the miss to come back. I went ahead and installed the front COPs, but I don't think the miss was coil related.

Everything seems fine. However, every once in a while I'll hit a big gust of wind and I get a very slight hesitation. It's very similar to when the low fuel light comes on. In the summer it's so rare I don't even worry about it. I've put 3k miles on it, and it's 99.9% good. This fall I ridden it on a couple of windy days. Today was very windy. It was missing and hesitating much of the ride. Usually in the 45-65 mph range in 5th gear. If I gun it, or shift down, or give it some choke it mostly clears up. If I hit an area with no wind, it runs perfect. I tried spraying carb cleaner around the carbs and intakes at idle, and could not detect a leak. I have taken the temperature of the cylinders near the spark plugs. I notice the left cylinders are slightly cooler (180 vs 200 on the right).

Any ideas why wind would impact how it runs? The air hitting the engine from riding down the road at 60 mph doesn't hurt it. It seems like it has to be a sideways gust.

 

[MaxMidnight]

Are the float chamber breather tubes installed and in the correct place?

 

[Fire-medic]

Any changes in the airbox?

 

[02GF74]

Any ideas why wind would impact how it runs? The air hitting the engine from riding down the road at 60 mph doesn't hurt it. It seems like it has to be a sideways gust.

No but this is one of the strangest problems to date.

My guess is that it's the sudden side to side movement that may be causing something to move so affect the fuel pick up in the carbs. .

Need to think about this, as you say it's immediate then rules out most of what I wrote.

 

[dbthomas]

The air box and filter are stock. I looked at some pictures/videos showing the stock location of the carb breather hoses and mine are definitely not in the stock location. They are basically just draped over the rear cylinders and I do not have the stays that should hold them to the air box. So that could be a possibility.

I pulled the air box to get a better view and I’m not 100% sure if the crankcase breather was attached. There is no clip on the hose, so it’s definitely possible it came loose. Also, there is a smaller nipple on the front bottom of the box with no hose attached. Should that have something attached?

I did inspect the fuel pump last year, but will give it and the lines another look. On a single gust of wind, the hesitation is immediate, so I wouldn’t think the fuel pump could cause an issue that fast. It does seem like a lean condition though, so too much air or too little fuel are likely culprits.

I might go ahead and order carb breather stays, crankcase breather clip, and fuel filter, and see if it helps. Thanks for the feedback.

 

[dbthomas]

I put the bike back together while I wait for parts. I made sure I got the crankcase breather hooked up well. Also, there is a cover in the bottom of the air box where the crankcase breather distributes to each stack. I was missing the center screw there, so replaced it. And I ran the carb breather hoses close to where they belong under the faux tank and loosely zip tied them in place. It looks like the factory stays that I'm missing have a wind deflector built into them, but the tank cover probably protects them a lot.

Unfortunately the temperature dropped about 30 degrees since my ride yesterday (40 degrees today). I started it up, let it warm up about 10 minutes, and took it on a short ride. It was very windy. I didn't experience any hesitation. It's supposed to be back in the 70's this weekend, so I'll give it a longer ride then, but I think it might be fixed. It's strange because I see some people saying they aren't running those hoses at all.

 

[MaxMidnight]

The air box and filter are stock. I looked at some pictures/videos showing the stock location of the carb breather hoses and mine are definitely not in the stock location. They are basically just draped over the rear cylinders and I do not have the stays that should hold them to the air box. So that could be a possibility.

IMO more than a possibility. The gusts are altering the the ambient pressure in the float chamber which is causing the hesitation..
What you need ar 2 x 1FK-14413-00-00 and 2 x 1FK-14414-00-00. Suggest you sort that issue before spending time (and money) on anything else.

 

[dbthomas]

Thanks Steve. Those are really the only parts I'm ordering besides the crankcase breather clip. I only ordered one each of the breather stays you listed, hopefully that is enough. Those are starting to be difficult to obtain.

 

[one2dmax]

DId you check the fuel tank vent? It's a tiny hole with the hose that's a lot bigger. Easily plugged and can cause issues when you get riding for a bit that can go away when you slow back down or pull over. One of the symptoms when it's bad enough is a whooshing sound as air enters the tank when you pull the cap (that's when it's getting really bad).

 

[dbthomas]

DId you check the fuel tank vent? It's a tiny hole with the hose that's a lot bigger. Easily plugged and can cause issues when you get riding for a bit that can go away when you slow back down or pull over. One of the symptoms when it's bad enough is a whooshing sound as air enters the tank when you pull the cap (that's when it's getting really bad).

There's definitely no pressure or vacuum when I pull the fuel cap. I'm pretty confident it's the carb or crankcase breathers. I'll get confirmation this weekend. Hopefully I'll get the proper stays and clip by then, but at least everything is where it's supposed to be now.

 

[3-Max]

Also, there is a smaller nipple on the front bottom of the box with no hose attached. Should that have something attached?

Nothing should attach here. I believe this is to drain any liquid that gets in the box.

 

[dbthomas]

Nothing should attach here. I believe this is to drain any liquid that gets in the box.

Thanks for the answer. I was hoping that was the case. I got the crankcase breather hose clip tonight and that was enough of a pain to install (even with the overflow tank moved out of the way). Carb breather retainers have not arrived yet.

 

[dbthomas]

Thanks for the help all. I put on 50 miles on a very windy day. Not one hesitation. It was definitely the carb or crankcase breather hoses, probably the carb breather hoses based on the fact that Yamaha put wind deflectors on the stays. Steve called it.

 

[MaxMidnight]

Engaging smug mode - pleased you managed to get it sorted.