Fuel issue

[83VR3711]

Ok....all was good for a while. I finally got her to a state where I can drive her daily to work. Acceleration and take off were great. After a few days, there started to be some lag below 3k. After a few more days of driving, it got to where it lagging below 4500 RPMs, the 5k and now it is at the point to where it will lag until 6k. After I reach 6000 RPMs, she shoots off like a rocked, but of course I have to shift and when I do, the lag or bogging down returns till 6000 RPMs is reached again. I am not sure where to start....I just had the carbs syncd and I cleaned the plugs. I just replaced the air filter and I have new wires on the way. Could it be the fuel filter causing my issues or do you think that I will have to clean my carbs again (3rd time in 6 months)? It seems the more I keep driving it, the higher I have to get the RPMs in order to get normal throttle response. also, Yes, I have been running seafoam. Please help....

[dynodon]

I don't think it could be the fuel filter or it would tend to bog down the higher the rev's go, since that is where you are using more fuel. Electric pump will send same amount of fuel no matter the rpms.

 

Be careful not to run too much seafoam. Follow the instructions, more is not better.

 

Any chance you got some bad fuel or even some diesel in there? That could cause some lower rpm problems that would clean up at higher rpms.

[skydoc_17]

It is my opinion that you are dealing with an electric problem. When you get that set of plug wires in, bite the bullet and put in a new set of plugs. There is no real good way of telling if a plug is good or bad. Back off on the seafoam when you put the new plugs in. Over use of seafoam WILL foul a plug. Just for grins, turn off the petcock for the fuel, and crack the screw that will let the Carb. bowels drain out. (Pic below, yellow arrow) Catch what comes out and examine the contents. If it looks clear, (no chunks or rust flakes) then you may have the dreaded TCI problem which is extra bad because you have the 83'VR and that TCI is only on the 83'. This is all assuming that your Carbs. are Synced., and Diaphragms are good. While you are changing the plug wires, (Which is going to require you to remove the battery and the battery box, use PB blaster or WD 40 on the battery box bolts) pull the plugs on the TCI and clean them with contact cleaner and put dielectric grease on them. When installing the new plug wires I use a squirt of silicone spray on the ends of the wires. It helps getting the grommet and the plug wire back into the coil. Pay attention to how the grommet goes on, it's directional. I remove the wires from the coils one at a time, the two rears from the battery box location and the two front ones from under the front of the fairing. Be REALLY careful not to drop the coil cap or the grommet, Most Yamaha dealers don't keep these items in stock. If you have questions, PM me.

Earl

[Condor]

Didn't I read somewhere that the idle jets contribute fuel to the system for the first couple of thousand RPM over idle?? And the jet(s) may be plugged?? Just a wild stab.... Also you may be dropping a cylinder and new plugs may be in order??

[skydoc_17]

Hey Jack,

The Idle Circuit pretty much kicks out at 2000 RPM's. In the pic I posted above, the red arrow is pointing to the Idle mixture screw. (use PB Blaster or WD40 on these screws BEFORE you try to turn them) Lightly bottom that screw out by turning it clockwise and then turn each of the 4 screws (one on each Carb.) out 21/2 turns. This is a good start point. I use a digital Tach. to fine tune them but the problem he is describing is not due to this part of the Carbs. but it doesn't hurt to have them set right.

Earl

[Yammer Dan]

I would try new plugs first and keep my fingers crossed.

 

Then wiring. Could be just time for new wires.

 

Then check heat of exhausts when first started to see if all firing same.

 

Then TCI. If it is TCI left front cylinder will show a lot colder than others when it is started.

 

Hope you have found it before this.

[rhncue]

Didn't I read somewhere that the idle jets contribute fuel to the system for the first couple of thousand RPM over idle?? And the jet(s) may be plugged?? Just a wild stab.... Also you may be dropping a cylinder and new plugs may be in order??

 

I would have to agree with you on this. I definitely believe it is dirt in the carbs. May be the tank is rusting internally. The idle circuit not only works at Idle but all through the carbs range. The circuit adds to the amount the needle is allowing and to the main jet. Most of the jets in the carbs are very small and will clog easily from any dirt or varnish. This is not true with the main jet. It is very large compared to the others and in 50 years of tinkering with carbs I have never seen a main jet clogged. When under heavy acceleration or wide open throttle the main jet is what is allowing the most fuel to enter. It is for this reason, that I believe, that the carbs, and mainly dirty jets are the cause of this bikes condition. Since he states he has cleaned these carbs a number of times in the past and the problem re occurs there must be something causing it and it is either real old gas or dirt from the tank. I would drain the carb bowls, catching all of the gas and straining through some clean white gauze and see what is in the bowl. Just my 2 cents worth.

 

Dick

[83VR3711]

ok... so now I have replaced the wires and replaced the plugs. I appears that I have lost both rear cylinders. It is not due to the plugs or the wires. I did drain the bowls. #2, #3 and #4 drained clean. I was unable to get any fuel out of the #1 bowl. Something else I noticed...for the first time, I have started get the oil blow back in my air box. It has never been there before. Mind you, about a week or so ago, all 4 cylinders were firing. Any ideas?

[Venturous Randy]

If you are not getting fuel out of the carb bowls, you are not getting fuel into them. I would start at the fuel line from the filter and make sure every connection has good fuel flow thru it. You may have to make a connector that will bypass a carb and check them one at a time having fuel flow into a jar. An easy way to turn the fuel pump on is turn the ignition switch on and flip the kill switch several times.

If you are getting good fuel flow to each carb, you will need to go back into the carbs and see what the blockage is. You also need to make sure the pilot jets are not plugged and spark plug caps do not have corroded resistors.

Before your last post, I was thinking along the lines of a big vacuum leak somewhere. If you still have the YICS system installed, I would pull the hoses off and plug the ports. You can also have a big vacuum leak in the YICS box above the front head. A big vacuum leak will cause the diaphragms not to open well at lower RPM's, but as the RPM's get higher it will start coming on strong. You can spray starter fluid around the carbs and intakes and see if the RPM's change any. If they do, start looking for the leaks.

As far as the oil blow back, check your oil level and make sure it is not over full and make sure you are not getting any coolant into the oil.

Good luck and keep us posted. Several of my suggestions are problems I have encountered on my 83 in the last 13+ years.

RandyA