Engine misses at higher speeds.

[yamagrl]

84 VR

 

What would make the engine flatten out and miss when cruising at higher speeds?

 

It otherwise runs exceptionally well. It starts easily and requires no or little choke even when cold. You just kind of "turn it on". It has great acceleration, runs really smooth when at lower speeds. But when it gets to highway speed it flattens out and starts missing. It's like its starving for fuel. Open up the throttle and it seems to be better. Settle back down and it starts acting up again.

 

Before I did the second gear repair it did not have this problem. When I had the bike torn down for 2nd gear I only removed the carbs and set them aside. I simply reinstalled them when I put it all back together. That's when the problem started. So I pulled the carbs, completely disassembled, soaked in Berryman's Chem-Dip, rinsed, flushed every part, opening and orifice with Berryman's Carb cleaner, blew them out and reassembled with carb kits and new rubber plugs on the jet blocks. Re-used the coast enrichment and choke valves. Reassembled as per Damon Ferraiuolo's video. Float levels are spot on in the shop, (tied down on the lift in the riding profile, not on centerstand). So they should be pretty close to the same when riding.

 

The diaphragms had pin holes (light showed though) and so I did the "Plasti-Dip spray trick" (no light) hoping to get a couple of months out of them and defer the expense until a more convenient time.

 

It's kind of confusing though as to how it could be the diaphragms; before 2nd gear repair there was no issue but the diaphragms had holes, after the 2nd gear repair the problem began and remained the same after the holes were repaired with Plasti-Dip. It seems like it would have had some effect...something different.

 

I know I am going to need new ones. And if I have to bite the bullet and buy them now...so be it. But I'm hoping to ensure that the issue is not caused by something else and if so, fix it.

 

A few tidbits of related info.

 

The issue is the same whether I have the Ignitech and map sensor (Dingy) or the original TCI and boost installed. At the moment the TCI is installed.

 

I installed the new quick disconnect for the pick-up coils that Dingy included with the Ignitech

 

Fuel pump clicks pretty good when the key is turned on.

[bongobobny]

OK Yami, a few things come to mind. One thing is vacuum leaks. Did you replace the "O" rings on the bottom of the carb intake manifolds (Those 4 black tube things)? If disturbed, those rubber gaskets will no longer be sealed as with compression over a long period of time they change from "O" rings to flat bands. Also check for cracked rubber vacuum hoses, with the age of the bike I would have replaced all of them.

 

OK with the carbs there are two "circuits" the low speed and the high speed. Also, did you resync the carbs??

 

 

Questions, questions...

[yamagrl]

I checked the hoses but I'll check again. None were stiff and cracked.

 

I am drawing a blank about the orings you are referring to. Please reference them on the pats breakdown.

 

Sync?

[yamagrl]

Sync? How's this?

 

http://tapatalk.imageshack.com/v2/14/08/21/0d2a5f2f138a9c38773c65cad3cb36fe.jpg

[Venturous Randy]

Heather, this sounds similar to what I am dealing with on my 2nd gen trans/engine swap. The bike starts and runs good, but in comparison, it just feels like something is not right when I crank it on. It almost feels like it is dropping a cylinder or something, compared to the old engine. I also did not do anything to the carbs as the bike was running good and I did not want to add any more variables at the point of startup on the new engine. But with me, I had some carb problems because I turned the carbs upside down and replaced the drain hoses.

With the engine up to temp, spray some starter fluid around the base of the carbs and see if you have any change.

RandyA

[Venturous Randy]

I checked the hoses but I'll check again. None were stiff and cracked.

 

I am drawing a blank about the orings you are referring to. Please reference them on the pats breakdown.

 

Sync?

 

On the rubber manifolds that are between the carbs and the heads, there are O-rings that are under the base of each. If you have a leak in this area, when you sync the carbs, you are adding that air flow into the sync process. If you then plugged the vacuum leak and then went back and checked sync, it would be off.

RandyA

Edited August 22, 2014 by Venturous Randy

[bongobobny]

Thanks Randy, yes those are the ones...

[Neil86]

If plug wires and caps were tucked into chassis to R&R engine, are they still making good contact at both ends (coil and cap).

[videoarizona]

If it's not floats, I would think spark.

Agreed...check the wires at the coils. Thinking high speed miss...

In the old days I would suggest points...so check pickup coil feeding the ignition as well...

[yamagrl]

Based on all of the above suggestions, I'll...

 

1. Double check the vacuum lines, etc

2. The rubber manifolds were not removed but I'll check for vacuum leaks with starting fluid trick

3. Check the pickup coil connections. I changed the QD at the end of the wires coming out of the stator cover

4. If need be Ill pull the stator cover and check the coils. I had that all apart to facilitate stripping and refinishing the engine covers

5. Check the coils and plug wire connections. I had the coils off to remove some rust and paint the coil bracket frame in that area.

6. It has new plugs

 

VideoA, I'm kinda with you on this one. If it's not a vacuum leak or other obvious carb issue it might be an issue with ignition/pickup coils

 

I'll be working today and will have some time available this weekend to get back on it.

 

I have an opportunity to buy an 86 VR for $200. It is complete, but hasn't run for years. It will at least be a good parts bike. I think I'll go get it.

[rcbailey56]

I'd get that bike in a heartbeat. Even if the motor is seized, carbs gunked up or anything else like that, There is more than enough parts if the bike is complete to make it worth your while.

[Neil86]

You mention coil rack painting....I think there might be a ground point in that vicinity.

Might even be on one of the rack bolts? Make sure its clean (ie no paint) and in place.

Edited August 22, 2014 by Neil86