Timing adjustment

[a1bummer]

How do you adjust the timing if it's needed? The manual tells how to check it but not how to adjust it. I assume you need to pull the flywheel off to make any adjustments. Or at least pull the sidecover off if you can make adjustments through the flywheel. But I kind of dought that. Anybody have any pics? I've been having some pinging lately when under a load. Not sure if I got some bad gas when I went to the Dells this weekend. I'll try some high grade stuff from one of my normal stops before making any changes to anything though.

[pegscraper]

They aren't designed to be adjustable. I don't know what a guy is supposed to do if it is off or he's having trouble with pinging. But compression in these engines is so low that I figure it's pretty rare. Bad gas these days is a real possibility.

 

It can be done though. I advanced my pickup coil by 4*. I slotted the holes out in the bracket and moved it over. Then used loctite to hold the screws in place. I forget the dimension. I calculated it from the distance it is from the center of the rotor. It gave a little more part throttle responsiveness. (I'm assuming that 1st gens have a similar mounting bracket here.)

[Venturous Randy]

Bill, you may be correct about the gas, but before I did anything, I would check the boost sensor to see if it is working correctly.

RandyA

[mbrood]

Pegscraper,

 

That may be true for the 96 but for his 84... these four pickups would be REAL tough to shift in ANY way. The flywheel has two embedded magnets and they aren't changing location either...

 

http://bergall.org/temp/venture/alternator-a.jpg

 

a1bummer,

The timing is advanced or retarded by the boost sensor so if there's a problem, THAT is the unit to check. The service manual has the basic measurements... I find that most just need the first reading with the ignition on and not started... the manual says it should be about 2 volts... much higher or lower and you need a new boost sensor.

Edited July 23, 2008 by mbrood

[Gearhead]

I don't know what a guy is supposed to do if it is off or he's having trouble with pinging. But compression in these engines is so low that I figure it's pretty rare.

 

 

I'm not sure I'd call 10.5:1 "low compression".

 

Jeremy

[mtman]

Don't know how often you do it, but ya might try putting some SeaFoam in the gas and see if that cures the pinging... It's a cheap fix that can't hurt .

 

Wayne

[pegscraper]

Well, with four pickups like that, there may not be much that can be done.

 

I know what the manual states the compression ratio of these engines is. And I flat don't believe it. They don't start like a high compression engine. They don't run like a high compression engine. And an engine that truly has 10.5:1 compression will not run 87 octane gas, while these do. Don't believe everything you read in the shop manuals. These act more like 8.5:1 engines.

[Condor]

Yesterday while riding I got my first ping...ever.., but I really dogged it down when I did. These motors love high R's. Low R's is what caused it.

[Dano]

I know I can't roll on the power under 2 grand, it'll pop and backfire on me. Above 2k tho, is an ENTIRELY different matter!! Thats with 93 no-ethanol gas.

 

Dan

[Gearhead]

I know what the manual states the compression ratio of these engines is. And I flat don't believe it. They don't start like a high compression engine. They don't run like a high compression engine. And an engine that truly has 10.5:1 compression will not run 87 octane gas, while these do. Don't believe everything you read in the shop manuals. These act more like 8.5:1 engines.

 

 

Hmmm, what we need is for somebody out there with a head pulled off a VR engine to cc the chamber (and any piston dish, of course)! Time for a science experiment...

 

Jeremy

[Condor]

I know I can't roll on the power under 2 grand, it'll pop and backfire on me. Above 2k tho, is an ENTIRELY different matter!! Thats with 93 no-ethanol gas.

 

Dan

 

Could be the boost sensor not doing it's job?? Or... maybe a leak in the sensor vacuum hose?? Have you ever tried to apply manual vacuum on the boost at idle to see if the rpm's change any? And what gear are you in below 2K. My '83 will buck, snort, and get really pissed off if it isn't in 1st or 2nd...

[Dano]

Gotta try that boost sensor thingy, even have to do it off the line, so its consistent across all gears. Tried the carb synch, wasn't it.

 

Dan

[a1bummer]

OK. I don't have my manual in front of me... where is the boost sensor?

 

I guess I just assumed that like any other engine I've ever seen, (aside from the newer distributorless engines in cars, etc. these days), that these would have some sort of adjustment in the timing. So does that mean there is a computer that controls the timing?

 

I ran some Seafoam through a couple months ago when it was not wanting to run on all four. That took care of that problem.

 

I put some new fuel in today and went through 1/2 a tank. Didn't hear anything. Of coarse it didn't have the load it had this weekend and the weather was much cooler and not as humid.

 

I also know I need some new plug wires and caps. Don't know if that would make it ping though.

[BradT]

Hmmm, what we need is for somebody out there with a head pulled off a VR engine to cc the chamber (and any piston dish, of course)! Time for a science experiment...

 

Jeremy

 

Had the 86 apart before. Didn't take any measurements.

 

BRad

[Dano]

Yep, think its that boost sensor thingy. No reaction whatsoever when applying vacuum or applying pressure to the tube.

 

Boost sensor thingy is mounted to the left of the TCI, bottom side of bracket. Follow the little hosey thing that comes off of carb #2 (front left) up into the guts of the bike. Where it ends, thats the boost sensor thingy!

 

Now I gotta get me 1 of those.

 

Dan

 

Hummm, just wondering if the little one way valve in the line could be stuck closed???

[rhncue]

Yep, think its that boost sensor thingy. No reaction whatsoever when applying vacuum or applying pressure to the tube.

 

Boost sensor thingy is mounted to the left of the TCI, bottom side of bracket. Follow the little hosey thing that comes off of carb #2 (front left) up into the guts of the bike. Where it ends, thats the boost sensor thingy!

 

Now I gotta get me 1 of those.

 

Dan

 

Hummm, just wondering if the little one way valve in the line could be stuck closed???

 

There is no one-way valve in the line. That is a restrictor so that the vacuum is consistent instead of pulsating from the engine. The boost sensor is pretty difficult to get to as the battery holder and such must be removed and it's bolts are usually well corroded from acid. Those little sensors are pretty expensive to buy from Yamaha. You may want to try to repair yours. Some can be repaired and others can't. Bad part is that the bike is down while you are trying to repair.

 

Dick

[Condor]

Dan Hummm, just wondering if the little one way valve in the line could be stuck closed???

 

It's a restrictor, and yes it can become plugged. See if you can remove it from the hose and spray some carb cleaner through it. It's the same set up they have for the CarbTunes. It just smoothes out the pulses. I've had to clean out my Carb Tune's on occasion.

[Gearhead]

On the boost sensor: now, mine is an 87 and these comments apply to most models, but I know 83 and maybe 84 is a little different.

 

Yes, the timing is controlled by a computer called the TCI. It has a RPM vs spark advance curve programmed into it. In addition, it does vacuum advance for economy, accomplished via the boost sensor. This part outputs voltage based on the amount of vacuum applied to it from the carb stub. When vacuum is high, it sends some voltage to the TCI that tells it to advance the curve for better economy under light loads.

 

If the sensor (I would actually call it a "vacuum sensor" if it were up to me) is faulty (and many of them are), the timing won't advance under light load, but will stay on the more retarded "baseline" curve which is best for heavy throttle. This will not cause pinging, but will cause MPG to fall. Therefore, I wouldn't suspect the boost sensor if the bike pings.

 

One more thing. I'm pretty sure that high vacuum will NOT increase the timing at idle. I think the TCI is programmed for the vacuum advance to kick in somewhere around 2k rpm. So to check it, you need to run your idle speed up to 2k with the thumb screw, THEN pull vacuum on the line to the sensor.

 

Jeremy