Sick (and I don't mean in a good way) GTR.

[schlusselmensch]

Over the last 5 years or so I've brought a 350GTR back to life, mostly with Richard's help on the parts front and eBay as well. At any rate, the bike is in quite good condition, not a show winner, but certainly presentable. Only problem is that it refuses to run with the enthusiam that GTRs were famous for. I bought the bike from a fellow who had suffered a head injury in a motorcycle accident and he could not really recall what work he had ever done to the bike. It became clear after quite a while that he had had the bike to pieces and put it back together, and this was after the head injury from the look of it. To be fair, perhaps someone else did it.
Bolts were missing in the weirdest places and the electrical wiring was full of wires of different colours hooked up. In addition, someone had managed to engineer the most miserable transient ground that I've ever had the displeasure to ring out of an electrical harness.
But it just doesn't have the urge it should have. EVERYTHING is in good condition. I'm beginning to suspect the rotary valve timing. It looks possible to get them wrong, judging by the parts book? Does anyone know the specifications? I was able to find the timing on the net years ago but have had no luck recently tracking it down. The bike has very pronounced carb roar but this may be the nature of the beast? That's about the only other symptom other than its weak acceleration.
Best regards to all the Bridgestone fans,
Ken

[OldSwartout]

The rotary valve opening (and other port timings) is shown on P. 79 of the service manual.

Rotary Valve Open Period = 242° to 62°
Rotary Valve Open Duration = 180°

That could be a problem, but look for other things, too.  You've probably already done this, but check to be sure both carbs fully open and the ignition timing is correct.  Check to make certain the exhaust, especially the baffles, are not plugged.  If the bike has few miles on it (under 25,000), the baffles are probably OK, but if the bike was apart for awhile in a barn or shed, it is entirely possible there are mouse nests in one or both mufflers.  I've also seen grease rags left in exhaust systems (put there to keep the mice or nuts and bolts out, then forgotten).

[schlusselmensch]

Many thanks for the disc info. Anything you can think of, I've done. One muffler is NOS from Richard, the other has been checked and is fine. Carbs are new, they were installed because of the transient grounding problem that affected the ignition at certain vibratory periods (mimmicked carb problems). Crank seals are fine, pistons and rings are fine, bores are fine. etc., etc., etc..
It just might be one of those pigs that Richard mentioned he'd run across once in a while, hopefully not though.
I'll check that the disc timing is correct. I'll be pleased if it's not.
Ken

[schlusselmensch]

I have to admit I did not check the site's service manual. My original service manual does not have the information. On page 80, only the thickness of the disc is mentioned. Page 79 has cylinder, piston, and crank tolerances.
Ken

[coxy]

are the carbs synchronized  .is the cable ok not stretched ? i had a xs650 before it died it idled well but  when you rolled on throttle she sputtered and was doey  that was a dirty main jet

[schlusselmensch]

Your help is appreciated but I am very sure of all the settings, clearances, connections, lengths, synchronizations, etc..
It has to be something a bit strange as I've seen a fair amount of weird faults in 45+ years of vintage bike, car, tractor, and airplane spannering.
Not to say that I can't have missed something but I've probably checked every bloody thing at least three times.
Once in a while you just run into a right swine to fix.
Ken

[old smokey]

Does the bike sound good when in neutral at idle and when rev'ed up? Or does it not even sound like it's healthy then?
Will it run when doing the prescribed method for setting the idle speeds by turning in one idle screw at a time and getting a decrease in rpm as one side cuts out?

[Toystoretom]

Your "carb roar" may be a clue so here are some thoughts:

The rotary valves are located with a dowel and really can only be installed with the correct timing. Possibly someone could have cut the rotary valves to modify them and from what I understand this just makes it run worse. I would think that any mods to the rotary valves would be apparent upon inspection.

Did they try some home made porting mods in the cylinders? This usually ends poorly unless you are a pro...

Bad crank seals..... or seals that can't hold at higher RPM's

Too heavy of an oil mix.. that actually leans out the mixture

I dunno.... wheel it into the shop here and we'll have a look 

[schlusselmensch]

I'll answer the last two posts together;
The bike idles and starts like a champ. Throttle response is fine off idle. It's just gutless on the road.
I'll tell you a story about oil percentages. I used to be in the UAV business (unmanned aerial vehicles), long enough ago that I'm familiar with the Northrop OQ19/KD2R aircraft. These used a 100 cubic inch four cylinder two stroke engine. The original recommended gas/oil mix was 4/1! And they ran just fine.
So I rarely look to a little bit of extra oil as a suspect in poor running problems. You are right though, more oil does lean the air fuel mixture. So I'm going to check the disc timing first off and I might drop the main jet down one from stock as we are almost a 1000ft above sea level. It does run quite a bit better in very cold weather (35-45 degrees).

[deisher6]

I put quite a few miles on a GTR in the 60's and had problems with power.  Diagnosed as the steel pin on the floats which had vibrated the holes in the carburetor out of round.  Cemented the pins in place with plastic aluminum and it ran well until I sold it in 69.

Just a possibility.

regards charlie

[Sno Jet]

That is a good idea about the carbs.  I noticed the same rounded out hole on one of mine.  They also sold bushing kits to fix the problem so it must be common.

I ended up buying a new set of carbs from Richard as I also had one that was cracked around the neck to add to the problem.

I have heard people swear by getting some new one's.  Process of elimination.  Harry

[old smokey]

Here is a link for an old photo I posted.
I only noticed this damage because I decided one day to turn the engine over with the carb off and happened to see the rotary valve damage. I never thought there was a problem because of performance. Maybe your valves were intentionally modified for timing, but probably not poor performance because of damage.

http://bridgestonemotorcycleparts.com/index.php?topic=426.msg1138#msg1138

[schlusselmensch]

Yes, all of the bikes with carbs mounted sidesaddle like that were hard on them. My bike has a NOS set from Richard.

[reed]

schlusselmensch
On your GTR running have you done a crankcase pressure test.
What is the temperature of you down pipes when the engine is warm.
The driven gear part number 2411-9000 i would like to see a picture
of the alignment mark on the gear, some where marked wrong so your
Timing would be out etc.
Thanks.
Steve.

[schlusselmensch]

Which timing would be out? Ignition or disc timing? I set the ignition timing on my 2 stroke bikes with a dial indicator at the recommended distance so I can't fathom how that'd be out. I believe the mark(s) you refer to is/are there simply to ensure that the points cam operates in the range that permits proper adjustment of the timing within the constraints of the slots in the points plate.
I wonder if there is any chance that the disc valve drive collar pins could be "off" a number of degrees from the factory. I think checking the disc timing is something I should do before fiddling with anything else. I have run across misindexed parts more than a few times. The loud carb roar makes me suspicious.

[schlusselmensch]

Sorry I don't know the downpipe temperatures, my super duper infrared sensor gun died a while back and haven't replaced it. I will tell you that both pipes would remove about the same amount of skin in about the same time.
Last year, I rode the bike when it was just above freezing and it ran much better, with noticeable improvement in acceleration.
I think I must try some smaller main jets if the disc timing proves to be correct.
With the as delivered to dealers 140 mains it ran slobbering rich.
With the after break in 130 mains it improved quite a bit but is still sluggish.
I think I'll order some 120 mains.