Plugs or Carbs?

[MikeZ06Allen]

Oh look another spark plug/carb thread. I have searched and could not find anything conclusive. So here is the scenario:

 

Bike has been sitting for about two weeks while I waited for the rain to clear out and for Rick to do is magic on my seat. I put in some SeaFoam (about 6 oz) at last fill-up and prior to letting it sit because I wanted to clean the fuel system some more when I got the chance to ride again.

 

Put the seat back on last night and decided to take it for a spin and top of the gas (took 1.8 gallons). When I started the bike no issues however as I rolled on the throttle there was hesitation and what sounded like misfires until I got the rpms above 4K. This got a little better as the engine warmed up but never went away entirely. Got back home and let it sit for the night.

 

This morning, with a very pleasant day ahead, I decided to ride the bike to work. Again bike started fine but same symptoms as last night. So as I am leaving from a stop the engine stumbles and as I twist the throttle the hesitation is there but it will accelerate just not really that quickly. If I hold a constant throttle at anything below 4K rpm there seems to be a surge folowed by a miss. Now if I apply the choke the surge/miss goes away but throttle response gets very sluggish.

 

My gut feeling tells me this is a carb issue but I think I also need new plugs as the ones in there were in a very rich condition for over a month worth of riding.

 

Recently, Skydoc and I replaced the carb diaphragms, installed the needle valve shim mod and tuned the carbs with a carb sync and other sundry adjustments. I have run plenty of SeaFoam through the system so advice other than add SeaFoam please. When sitting ( not under load) bike revs fine.

 

Any advice is welcome.

[Venturous Randy]

I would change the plugs and I get great service out of cheap Autolites I get from Advance Auto at less than $2 each.

RandyA

[bobcat]

I agree with Randy...I'd change those plugs if for no other reason than to eliminate them as the problem. (They just may be the problem.) While you're doing them I'd also check the plug caps. Possible corrusion in the caps can cause the type of problem you've described. I changed my caps a few weeks ago and got rid of a low level miss thats been aggravating me for months..

[Monty]

Yup, sounds like plug fouling. I always change plugs after a good Seafoam treatment, as it tends to foul them out.

[GaryZ]

Your symptoms sound like you are running on three cylinders instead of four. Start the bike (cold) and let it run for a minute or two. Shut it off and carefully touch the exhaust flanges. If one is still cool, it's not firing. This narrows down your problem. Pull the plug and inspect. If it's not firing, it will probably be wet with gas.

[Condor]

If the plugs don't clear up the problem, I'd vote on a wet TCI.....

[MikeZ06Allen]

OK folks all very good suggestions both in PM's and replies. I will change the plugs tomorrow as well as reverse my needle valve shim mod. If these don't clear up the problem I will pursue further.

 

Although I have to admit a wet TCI is a little on the far side of what I would suspect as the bike is garaged and hasn't seen rain since I have owned it but not entirely out of the realm of possibility I suppose. Thanks everyone I will report back.

[MasterGuns]

Mike, I, too, installed that needle shim mod and all it did was make my bike (86 VR) run extremely crappy. Went back to OEM settings within a couple days, and immediately it was corrected. These bike are notorious for running lean to begin and has been exasperated further by the crappy ethanol added to fuel blends. Move the needles further inward and all you're doing is leaning it up even more. Food for thought. One thing that convinced me the needle shim mod was wrong was just after installing it and taking it out and it running at 10 of 10 on the crappy meter, I taped up the intake opening on the airbox with some duct tape and took it out again. Ran great. Undo the shim mod and report back please.

[greg_in_london]

These bike are notorious for running lean to begin

 

Your mileage may vary as they say, but that's not my experience. Non-controversial comment is to say to look at the ends of your silencers - mine are black and running rich. Less so now than before, but it certainly does not run lean. If it did, we might get good mpg. As it is, I've boosted my sidecar & trailer mileage to 35mpg (imperial) from 30. I don't think the needle mod has made it lean, though.

 

Obviously, undoing the needle mod is a 20 minute change to check it's not the problem, so is worth doing for the sake of peace of mind, but could be worth switching back for the sake of saving a few cents, although your petrol is so cheap you don't know how fortunate (profligate - oops - slipped there) you are.

If you DO have to pull the carbs apart, check the rubber bungs in the jet blocks AND the o-ring around the nozzle (that the needle slides in). If you wonder if this is worth checking, pull the air box off and start the engine and decide if you can see petrol flowing out around the needle - if you can it's not atomising and not working as per design.

 

My first thought on reading your post was that it sounded as if your problems started when you filled the tank and that you may have had some dodgy petrol. Draining the tank is a pia, so just run it and see if it gets better...

[MikeZ06Allen]

OK guys, Problem solved and it did indeed turn out to be the needle valve shim mod. Here's a blow by blow of what I did to fix the problem.

 

1. Took the carb sliders apart and put the stock needle valve shims back in (man I glad I kept those suckers) . While I had it apart double checked the diaphragms' (new with only a couple of miles on them) orientation. All parts were still squeaky clean; reassembled each carb.

 

2. Took the bike out for an oil change at the local Yamaha dealership. Bike ran great with no hesitation or stumble.

 

3. Got the bike back home and let it cool for a couple of hours and proceeded with a plug change. All plugs were more white than tan or brown (indicative of a lean condition). If anything I would have expected a darker color because of the SeaFoam treatment. Luckily no metal detected on the electrodes so I think everything else is fine.

 

Synopsis: I believe for some folks the needle valve shim mod may work perfectly fine but the low miles on my bike means the orifice in which the needle valve seats has not worn enough (or perhaps the ethanol additives have swollen the o-rings) to take advantage of the mod. Thus causing my bike to run leaner than anticipated. This is my opinion and I can not substantiate without having an exhaust gas analyzer.

[Venturous Randy]

Synopsis: I believe for some folks the needle valve shim mod may work perfectly fine

 

I have been very pleased with the needle shim mod that I did. Yes, I did have to tweak it in a little as the 1st try made the bike run crappy. But, now I am seeing mpg's up to 48 if not running 75mph down the interstate. Before, 42mpg was a real good day. Also, I run it hard a lot and really can not tell power is down at all. I will bet if you tweaked yours in a little, you would also see an improvement with the bike still running great.

RandyA

[MikeZ06Allen]

Yes, I did have to tweak it in a little as the 1st try made the bike run crappy.

 

Exactly how did you "tweak" the mod?