DOHC Highway WOT Issues

[doodsaibot]

Hey guys, the other day I went for a nice ride and was unfortunately pushed onto the main highway that is undergoing perpetual construction not to mention the nightmarish traffic (again this was not my choice to hop on there.) At any rate, I was forced to run at WOT at many times out of necessity to avoid many of the numbskulls in traffic. I was able to exit after 15 miles of running WOT or at least close to WOT. The bike bogged down a bit as I was pulling into a parking lot. The idle promptly fell dead. After checking the bike over for about 30 seconds I started it right back up. Rode it home for another 20 minutes at normal speeds on the back roads and it did fine.

The highest RPM I hit was 8,000 in top gear when I was on the highway. I did a thorough check over of everything I could think of. Nothing wrong from what I could see. I was pushing my bike hard just to keep up with traffic although I hated having to do that.

Did the engine get too hot? Was there a vacuum issue at heavy use of the WOT? The spark plugs only have a couple hundred miles on them, carb has a good sync, oil level is good and was changed a couple hundred miles ago. Haven't ridden since this incident but I was planning a decent trip this weekend and was hoping to get this issue resolved before I set out again. I have never had to run the bike that hard to keep out of trouble so I'm not sure what's up...

 

[16VGTIDave]

So, you were running around 80? About the rated top speed of the bike? If that is the hardest you've run the bike, it is possible that you have the idle mixture set a bit rich and with the engine at full operating temp, the plugs may have loaded up once you got off the highway.

Running WOT for an extended period may also have shown issues with your petcock. I know that I have problems with my petcock and if I have to run the bike hard, like highway speeds into a headwind, I switch the petcock to prime to avoid starving for fuel. Also consider checking the venting of the gas cap. You might have developed a vacuum in the tank. Sitting for a minute would have allowed some engine heat to warm the tank, vaporize some fuel and build some pressure.

That is all I can think of right now. But don't fret, your next time on the highway won't be as nerve wracking.

 

[doodsaibot]

Yes I was running at 80-85 MPH. I have moved that fast before but only for a period of ten seconds or so on the tollway before I got to my exit. so in a roundabout way, yes that is hardest I have pushed that engine than ever before. I will check the gas cap for the problem you mentioned. I will re check the carb sync. I did that last October and I was able to get the left and right sides of the manometer about an inch and three quarters of each other. I put new rubbers in the petcock during the summer but they may yet be due for another swap.

 

[drewpy]

80 -85 is fine, did that for 600 miles on the sohc.

My friend has the dohc and he was with me all the way to shropshie (50 miles) at 90 -100 mph ( I was on the fz600)

avery now and then engines need an Italian service to clear out all the crud in the engine.
so long as you run a fuel filter, you should be ok

 

[doodsaibot]

I checked through everything I could think of. The carb sync is still on point and the petcock it is great shape. Didn't notice anything out of the ordinary with the gas cap. Then I came to the spark plugs that I had changed a little while back. They are DR8ES-L which is the recommendation in the manual. The placard on the side cover of the bike indicates D8EA. I figured they were basically the same thing and I could run either one. So today I decided to spend a few bucks and get the D8EA. Sure enough, I rode 75 miles total on the highway, mostly at top speed and did not have an issue, which brings me to my next question. Why didn't the DR8ES-L plugs work correctly?

 

[drewpy]

The L means 1/2 heat range hotter