Potential overheating?

[oliver750]

Hello,

Just picked up my new 1974 tx750. Based on vin, it's one of the wine red models from Japan. The bike and I are in Oregon, USA.

So far, the bike has ran well but it appears (to me) that it is overheating in stop and go traffic. The bike will be idling but when throttle is applied while clutch let out, the rpms decrease and the engine essentially doesn't provide any thrust. It will keep this up for a minute or two and then the bike will die.

When this occurred, it was slightly raining and the drops landing on the engine immediately evaporated. Engine was too hot to touch so I assume I'm looking at an overheating problem.

After waiting about 10 mins, I was able to start bike and ride home another half mile but bike was still behaving sub par when parked.

-does this sound like the cause would be overheating? If so, is this common? Any way to fix/prevent this from happening?

Recently, the bike has had carbs redone, new petcocks. It starts easily and runs well in all other situations.. thanks for any help/ideas!

[jayteenz]

Welcome to the forum Oliver.

Your problem sounds like a fuel issue to me. If it was overheating badly you would talking about engine seizures and terminal problems ! These engines do run hotter than most though and yours should be fitted with an oil cooler (being a later model) to help with this issue.

The fact that the carbs were recently "redone" makes me think they have not got things quite right as it sounds like it's running lean - too much air and not enough fuel. Can you take it back to whoever serviced the carbs to see if they can remedy things ?
Could also be an ignition issue as the coils on these bikes are not great and if your's are the originals they will be very old and possibly breaking down as they heat up.

Cheers - JT

[scrambler]

Jay, as far as I know, cooler was an additional extra that could be purchased for the TX, they didn`t come out from the factory like that. Running lean indeed may cause such symptoms and can lead to overheating. I`d look at the spark plugs first, they will tell you if the engine runs lean. 

[farmrjohn]

Another issue the engines can have when "hot" is coil failure. My 74 would exhibit issues idling/accelerating when hot in stop and go traffic and new coils solve the problem. Good call to check the plugs.

[oliver750]

Jay - sounds like adjusting carbs is worth looking into. Do your know if there is a service/owners manual for the bike on this site? I can't find one and would love some diagrams of the carbs etc.

Scrambler - You are right, I don't have the oil cooler. I'll check plugs later today..

Farmrjohn - Haven't heard of that as a potential issue yet but I'll research more for sure.

[jayteenz]

Oliver - the only manuals I have seen are on Ebay (I just searched there and there are a couple of options for sale at present). It also pays to read all the Yamaha Service Bulletins (see that section on this forum) as Yamaha made of lot of changes to the bike in its short life span.

[oliver750]

Update - pulled the plugs here are some pics of them. The lighter colored tip plug is from left carb. Also including a pic from the left carb intake. Bike still not running right with new plugs, no difference as far as I can tell. Also included some carb pics. Thoughts?

drive.google.com/file/d/0B4ULoB_CbhCVNVEzRTluR0JnRHM/view?usp=drivesdk

drive.google.com/file/d/0B4ULoB_CbhCVLXVXcnF0dWxXRTA/view?usp=drivesdk

drive.google.com/file/d/0B4ULoB_CbhCVVXA4VXl2cENjRTg/view?usp=drivesdk

drive.google.com/file/d/0B4ULoB_CbhCVTWlwSFE3UUVpTFE/view?usp=drivesdk

drive.google.com/file/d/0B4ULoB_CbhCVbktpRms1N0NJOFk/view?usp=drivesdk


drive.google.com/file/d/0B4ULoB_CbhCVS0JnZ0lYOUNNNGc/view?usp=drivesdk

drive.google.com/file/d/0B4ULoB_CbhCVNnZfSGM5akQwWGs/view?usp=drivesdk

[pewe]

Hello,
Black spark= running too fat. Which size of jets are in the carbs?
Greetings
Peter