Running terrible at low revs when hot

[movenon]

After fixing the hose from the pet cock to the carb the bike still runs rough when it gets hot.

From what I an see from other posts and topics, it may be running very rich.

The plugs are all carboned up, all the same

The bike runs ok when cold, as it gets hotter it runs worse

All the hoses are now sorted.

My next plan is to strip down the carbs and check the jet sizes. Any suggestions on how far to go with the resizing? Not sure what's in there at the moment

Cheers

Cleaning and rebuilding the carbs is always good and truthfully is probably what it needs.  How does the the idle react when you adjust the idle air screws ? Did you do a blip test ?  Have you synced the carbs ? If you clean or rebuild the carbs you will need to sync them to make it run smooth.

On the carbs I recommend to go into the "File" section and read through the carb information. There are some good "how to's" in there. While the carbs are pretty basic there is a lot of little details that can mess with you. Randy at RPM (racerrad8) can help you or suggest jets for you. Send him a PM or e mail from his web site. http://www.rpmracingca.com/products.asp?cat=24 .

Also lots of posts on carbs to read through. Try the Search function and scan those. Ask questions as you go. Pictures do help when trying to describe something. I never did pick up where you are located. Perhaps there is a FJ owner in the area that can also advise you.
George

[Dazza57]

Hey Rusty, I'm not an expert by far, but have just gone through a full rebuild of the carbs, became a character building exercise. George gives great advice, and there is heaps of info in the files on carbs. The "blip" test and the idle mixture is a good place to start. When I did mine and the beast actually ran, I had to do the synch before she actually ran "RIGHT" Kookaloo !!

Good luck, and you know where to find us.

Cheers, Dazza

[Rustyas]

Guys,

Just had a thought

I haven't mention the fact that the bike uses oil in a big way, probably a litre of 15/50 per 1000klms.

Trouble is it doesn't blow smoke, any smoke at all.

I am assuming the rough running is due to it running very rich and I'm going to look at the jetting. The spark plugs are all covered in thick black carbon

BUT could the oil be burning and depositing on the plugs causing the thing run rough?   

Should I pull it down and replace the rings?

Or should I just burn it?

[Harvy]

Could certainly be the cause of the rough running due to the plugs being fouled - sounds to me like new rings at the very least are in order - that is a lot of oil being burned.

Harvy

[Pat Conlon]

Have you done a warm compression test to see what you got?
High mileage FJ's use oil....and they still run, seemingly forever. You could be loading up your plugs with oil from leaking piston rings....or you may just need to clean out your pilot jets, jet nozzles and idle circuit.

Which would *you* do first?    

[poker007]

 Do you know when the last Valve Adjustment was done on your FJ  ?

[Bminder]

I agree with Pat.
Here was my experience with my '92 that had been sitting for 3 plus years:
Randy cleaned the carbs, I tried to clean the tank.
Ran ok when cold, but as it warmed up it ran poorly under 2500 rpms or so, and would not idle very long. Above 2500 it ran great.
Cleaned the pilot jets mulitple times because they were still getting plugged from residual crap in the tank.
Randy sent me new pilot jets the next size up.
Still did not want to idle very long and Randy diagnosed that the cams were out of time.
Put the cams back in time.
Runs like a champ... almost. Might need to play with the idle mix screws a little. It chugs sometimes at steady low rpms.

[Rustyas]

Hey all, sorry for the delay, but other than stuffing around trying a few things  :ireful:there was not much to report.........Until now.

It finally got the better of me, I decided to start at the beginning and work my way through.

My plan was to remove carbs look at the jets and sizes etc and also pull it down and replace the rings. Between myself and my brother in law we reckoned we could have it disassembled in two nights, purchase parts required and re assembled in two nights, allowing for delays we reckoned we could get it done over a period of one weekend, five week nights and then another weekend.

Bugger me if when I open the air box, I found the air filter laying in the bottom of it, not up in place where it should be. Closer inspection showed the rubbers between the carbs and the barrels were not on  on the bottom and there was no seal at all

So where I thought the bike was running rich ( as the plugs were blackend and all carboned up )  it would appear it was running lean!


All of a sudden it made sense: motor running hot, idling at high revs, lack of power down low. missing and coughing at low revs..... had to be due to running lean


I fixed the air cleaner, "manufactured" a wedge to hold it in place ( clips were missing), spent hours trying to get the rubbers to seal

finally got it all together and it works!!!

Where as before it was 2/10 - 4/10 on a good day it is now 7-8/10. still has some minor down low issues, but for now good enough to enjoy the ride.

Thanks for all the help fella's. I"ll keep you posted

[novaraptor]

  Gotta love it when it's the simpler things.. Good scootin' to ya!

[movenon]

In trouble shooting, "take nothing for granted" always start with the simple stuff first and put things into spec.. Glad it was a no expense fix. 
George

[oldktmdude]

  So, where is all that oil going?   

[Rustyas]

 So, where is all that oil going?    

Good question I'm assuming that due to the motor running hot, recent rebuild etc it just was burning it at a higher than normal rate. I was adding about 1 Litre about three times a fortnight.

Since I "fixed" it seems to have slowed the usage dramatically. I can see by the sight glass that it is dropping but no where near as much as before. The bike does about 250-450 Klms per week, depending on work. so I figure if I need to top up once a month that would be OK

[fintip]

Sounds like a botched rebuild to me... I'm no expert, but I've had a rebuilt bike engine before done right. No oil burning issues. I've also worked with a guy who did his own rebuild, his first one--it wasn't a flawless job, and it burned oil.

Cross your fingers. Also, post some pictures of your plugs. Also, maybe some basic spray adhesive from a fabric store might help you get a really decent seal on your air filter, without being a permanent fixture.

How many miles on the bike since the rebuild?

[Rustyas]

Seems I have developed an oil leak  

How do I post pics here?

[Harvy]

Seems I have developed an oil leak  

How do I post pics here?

When you want to add a pic to a post, first the pic has to be hosted on the web somewhere (not just on your pc).

Then you use the image button:



and post the link to the hosted image between the img and /img with the brackets around those 2 codes. The above was done like this:

Code Select Expand

[img]http://fjowners.com/gallery/6/22_19_12_13_7_03_08.png[/img]

Harvy