Author Topic: Anyone ever heard of this on a 750? FIXED (Read 6960 times)

HOSA · « **Reply #25 on:** March 25, 2013, 08:04:22 AM »

Hey, did you ever figure out what was wrong?

Doug {HOSA}

Graydude · « **Reply #26 on:** March 25, 2013, 08:19:57 AM »

I'm really close to having it running right. I will report back with what I found. Stay tuned!

Red Good · « **Reply #27 on:** March 25, 2013, 08:23:31 PM »

When you do your compression test are you holding the throttle open ?

Graydude · « **Reply #28 on:** March 25, 2013, 11:21:01 PM »

Yes I do open the throttle wide. I still can't get cylinder #2 to fire. New plugs, spark is good. I replaced all the clamps on the rubber boots, both sides. I figured out I had a vacuum leak. Here is what it does now. Starts immediately on full choke . All four cylinders fire as they all warm up to about 225 degrees. When I take it off choke, cylinder#2 starts to cool down while the rest stay above 200. I don't think I have a vacuum leak anymore as the rpm does not go up at all when I spray starting fluid around engine side boot or carb side. But when I take it for a spin, I get a miss and cut out from that # 2 cylinder. Remember, it runs strong on the choke. When it's all warmed up and I pull the choke on full, the idle goes up. Shouldn't it die on full choke when warm? I've tried all the suggestions offers here and still can't figure it out. I refuse to give up. I maybe divorced by than but I some things are really important to me

lucky · « **Reply #29 on:** March 26, 2013, 01:32:56 AM »

Thanks for clearing up all of those comments.
On the internet it is hard to tell some things about what is going on.

I agree with Scottly about spark plug issues.

When you said that you turned the head upside down and poured oil (or light oil) into the head to see if they would leak over night, that could have ruined the spark plugs.

I had a similar incident. I put some Seafoam in my cylinders one winter and then when I started it up the next time, it ran poorly and one of the cylinders was cold to the touch.
I removed the plug on the cylinder that was cold and put in a different used spark plug and it ran perfect. Somehow the plug that was in it which was relatively new got damaged my the Seafoam in the combustion chamber when it started up.

Just a guess.

K3Owner · « **Reply #30 on:** March 26, 2013, 04:48:19 AM »

Quote

But when I take it for a spin, I get a miss and cut out from that # 2 cylinder.

You weren't clear on when exactly it does this but the rest of your message suggests an idle circuit issue - clearing up on choke could also be an indicator of this. I suppose it accelerates well (mains) but cruises with a miss (idle/transition)...blasted carbs.

Oh, regarding the low compression - consistent 90-100 psi with full throttle and no choke - look to your gauge. I purchased a cheap Harbor Freight kit because my old reliable auto gauge couldn't adapt and got similar readings on my 550 with fresh head and 8,000 miles. Scared the crap out of me! Old gauge and HF adaptors from the kit - 150 psi. Sometimes, the Chinese don't get it right

Graydude · « **Reply #31 on:** March 26, 2013, 01:56:06 PM »

Thanks guys. Carbs are surgically clean. I tore them all apart a few weeks ago after rebuilding them last fall. Everything was in spec. The only issues I detected were the carbon build up on both the pilot screws on number 2 and 4, the same two that were not running consistently. I thought I had found my smoking gun! Cleaned them up and set each screw at 1 3/4 turns which is what Honda says to to do with the F3 motor and 110 mains. Cleaned all the ports again with carb cleaner, blew them out and reassembled. Number 3 did come back on line but still no improvement with number 2.

Sure feels like a vaccum leak when I ride it and it is off the idle circut. Has that popping and surge, not on deseleration but on steady throttle. Where else could I be getting a leak? I don't have gaskets on where the header pipes join the head. Is that a source?

Old Scrambler · « **Reply #32 on:** March 26, 2013, 04:45:04 PM »

YES...........very well could be. And without gaskets your just asking for trouble.

Graydude · « **Reply #33 on:** April 04, 2013, 05:28:10 PM »

Ok. I've completed all the suggested fixes. Put gaskets on the exhaust header and even replaced the carb boots with some that I soaked in acetone for 24 hours. They are as soft as a baby behind. Can't detect a leak anywhere but the damn #2 cylinder is not running. All four cylinders run on full choke. Soon as I let the choke off the #2 stops combusting. I can pull the plug wire and their is no difference, still running on three cylinders. You can hear the popping and I know is running lean but I can't find an air leak. It has to be on the #2 carb but where?
What am I still missing?

scottly · « **Reply #34 on:** April 04, 2013, 06:32:08 PM »

Quote from: scottly on March 06, 2013, 06:50:05 PM

Uh, what do the spark-plugs look like? Are they carbon fouled? Clean and wet? Clean and dry?

Don R · « **Reply #35 on:** April 04, 2013, 07:54:01 PM »

It sounds like #2 carb is acting up. Have you compared the fuel levels in the bowls visually?

steam-powered man · « **Reply #36 on:** April 04, 2013, 08:35:22 PM »

after sitting so long, you may have an idle circuit on #2 that is plugged.

sometimes compressed air/carb cleaner thru these circuits isn't enough. you'll probably need to mechanically clear the idle circuit(s) with a thin wire (guitar string). btdt, and it certainly won't hurt at this point.

754 · « **Reply #37 on:** April 04, 2013, 08:56:26 PM »

If you could swap carbs you would know for sure.. Might be a valve problem..burned or pitted.. That changesas it warms up..

Graydude · « **Reply #38 on:** April 06, 2013, 06:04:52 PM »

Update: found I was getting most of the lean condition from poor sealing carb boots. I had another set so I soaked them in acetone for 24 hours and turned out soft. I still have a lean condition so I'm replacing the o rings on the pilot screws. The o rings look shot. I also suspect the wrong size main jets in place from a carb swap I did last year. I currently run 105 mains. I have stock header but after market baffle. I'm going to go with 110 mains and see if that helps the lean condition. I'll report after this attempt.

scottly · « **Reply #39 on:** April 06, 2013, 08:10:21 PM »

What do your spark plugs look like?

Graydude · « **Reply #40 on:** April 07, 2013, 11:26:17 AM »

The plugs are dry and blackish. Not oil black but I think black from running lean.

754 · « **Reply #41 on:** April 07, 2013, 11:28:22 AM »

Black means running rich..

scottly · « **Reply #42 on:** April 07, 2013, 08:10:58 PM »

Dude, you need to get your bike sorted out soon, so you can join CoachDoc on his way to 29 Palms for this year's relay!

Graydude · « **Reply #43 on:** April 10, 2013, 11:02:11 AM »

Believe me, NOTHING would make be high five more than having this baby running top notch. I'm just waiting on new carb boot clamps and 110 main jets to be delivered and then I'll know if I'm on the road or not!

Graydude · « **Reply #44 on:** April 28, 2013, 07:48:24 PM »

Happy to report i think I'm in good shape i got so many good suggestions from members and i want to say i really appreciate the feedback. OK, on to the details. Two major reasons I was running so bad. The first had to do with leaky carb boots. Pay particular attention to how the number 2 and 3 boots seal with the cylinder head. if you were like me, those two boots were about 1/4 inch lower than the 1 and 4 boots. problem was 1 and 4 boots would mate up with the cylinder head and 2 and 3 were not as close to the head as they should be. Consequently, those two cylinders, number 2 in particular, were sucking air causing a lean condition. I fixed the problem by not seating those two boots against the carb holder plate. That helped a lot.

The biggest problem was the poor performance at throttle. I screwed myself here. My bike originally came with a Karcker exhaust system. With this system, the carbs used 120 mains. Over the course of the last year, my Karcker rusted out and I obtained a stock four to one header and an after market tail pipe. Stupid me I thought since I was going with a stock four to one, I should go with the factory recommended 105 main jet. So I did. Bad move. Long story short is bike runs perfect with 120 mains again.

Bike runs great so I"m a happy camper. Thanks again to those who chimed in.

scottly · « **Reply #45 on:** April 28, 2013, 07:54:24 PM »

So now you can join CoachDoc, GreenHornet, Goldarrow, and Apexxn on the relay??

Graydude · « **Reply #46 on:** April 28, 2013, 10:44:53 PM »

maybe

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Author Topic: Anyone ever heard of this on a 750? FIXED (Read 6960 times)