Author Topic: i need help with carbs please (Read 3299 times)

pinnacle · « **on:** November 19, 2009, 05:27:11 PM »

i can"t seem to get my idle to settle down with idle screw completely backed off.i checked cables not binding,checked for vacum/air leak at boots don't have any,but #3 carb is acting diff than the rest it is puffing air and fuel out instaed of drawing it in i took a vid to show what i mean.could my timing be possibly off? can anyone suggest where i can look to solve this problem.the bike is a 1978 cb550k no filters on it yet as i havn't picked up some pods yet.

TwoTired · « **Reply #1 on:** November 19, 2009, 05:50:37 PM »

Video didn't work for me.

Have you vacuum synced the carbs yet?

750goes · « **Reply #2 on:** November 19, 2009, 07:16:27 PM »

certainly looks different than the others, might need to give it a bit of a clean - emulsion tube, main jet, idle circuit, float height.....I'd even check the tappet clearances...I'd do that first to confirm they are ok.

05c50 · « **Reply #3 on:** November 19, 2009, 07:31:33 PM »

+1 on tappet clearances. Looks like compression coming out carb.

................Paul

Hasenkopf · « **Reply #4 on:** November 19, 2009, 08:41:04 PM »

I would start with the basics first, compression check, timing, valve clearance..... What yousee may be a symptom of something else. and vacuum sync those carbs !!

Hush · « **Reply #5 on:** November 19, 2009, 08:56:54 PM »

That's definitely why the idles are high, #3 is gulping gas.
I'd pull at least the emulsion tubes on that carb and see if the tiny holes are blocked up, that gas is fair spewing from #3 and it should be a fine mist.
Then sync the carbs, you'll have to do that again when you have air filters fitted.

topgun · « **Reply #6 on:** November 19, 2009, 09:25:36 PM »

It might sound stupid but check that the hose coming out of the bottom of the bowl is not blocked had similar problem with a k6

pinnacle · « **Reply #7 on:** November 19, 2009, 10:26:40 PM »

well i checked that hose not plugged.so just out of curiosity any time you remove the cam and set it back in your suppose to redo your valve clearances again? do they change if you have not loosened the locknut or fiddled with the rocker arm?as i have not done the valve clearances again since removing the head to change the head gasket out.

TwoTired · « **Reply #8 on:** November 19, 2009, 10:43:26 PM »

The shop manual is quite clear about installing the cylinder cover and being careful to get all the tappet adjusters on TOP of the valve stem.
Tightening down the cylinder cover without backing out the adjusters almost guarantees that the adjuster is off the valve stem tip and further tightening pushes the stem sideways and bends the valve. The resulting bent valve then sticks in the head and can't close or move correctly. You will likely have to replace one or more bent valves in the head now.

Hush · « **Reply #9 on:** November 20, 2009, 12:20:02 AM »

Ouch I didn't want to hear that TT.

TwoTired · « **Reply #10 on:** November 20, 2009, 12:58:50 AM »

Quote from: Hush on November 20, 2009, 12:20:02 AM

Ouch I didn't want to hear that TT.

It's not the first time it's happened, sadly.
Pinnacle can easily disprove the possibility with a compression check. But, I expect the back spitting out the carb inlet is the result of an intake valve that can no longer close. And, those cylinder will have awful compression numbers.

pinnacle · « **Reply #11 on:** November 20, 2009, 11:51:05 AM »

When I installed cylinder cover I held up the tappets with elastics to make sure they were out of the way was would this still bend the valves

TwoTired · « **Reply #12 on:** November 20, 2009, 11:59:39 AM »

Can you absolutely guarantee that this didn't happen?

pinnacle · « **Reply #13 on:** November 20, 2009, 12:49:31 PM »

sadly no i can't unit i look at it,but before i tightened any bolts and released the elestics that were holding them i did eye them to make sure they were over the valve stem but i am going to open it up and check...thanx for the input T.T

pinnacle · « **Reply #14 on:** November 20, 2009, 04:07:29 PM »

Ok so I set the valve clearance but the puffing through #3 is still there.so here is my next batch of questions...is there any other possible fault that can cause this? And if not how do you diferntiate between a bent valve and a poor valve seat?can my timing be off anywhere I should check that would cause it?I removed the carbs and cleaned the jets and emulsion tubes so those are ok.

05c50 · « **Reply #15 on:** November 20, 2009, 04:11:10 PM »

It sounds like the best thing you could do now is a compression test to be sure that the valves are working properly. It won't matter much if the valve is bent or the seat is bad, both will require removing the head.

............Paul

TwoTired · « **Reply #16 on:** November 20, 2009, 05:08:26 PM »

Quote from: 05c50 on November 20, 2009, 04:11:10 PM

It sounds like the best thing you could do now is a compression test to be sure that the valves are working properly. It won't matter much if the valve is bent or the seat is bad, both will require removing the head.

............Paul

+1

pinnacle · « **Reply #17 on:** November 21, 2009, 12:24:10 AM »

one last inquiry when i removed the carbs this afternoon to inspect the emulsion tubes i noticed a second little spout beside the fuel inlet not hooked to anything is this just a vent for the carbs or is it suppose to be hooked up to something?

TwoTired · « **Reply #18 on:** November 21, 2009, 12:35:29 AM »

It's a pressure equalization vent. Normally had a tube that ran back and down between the engine and swing arm. The long tube kept dirt and most bugs from getting into the float bowls.

pinnacle · « **Reply #19 on:** November 21, 2009, 01:00:42 AM »

hey tt you think i would be better off doing a leak down test as opposed to a compression test to check for bent valves or poorly seated valves and would it be a more accurate reflection of the state of the valves or not?

TwoTired · « **Reply #20 on:** November 21, 2009, 11:51:52 AM »

Leakdown tests are more accurate. Particularly when all the cylinders are at operating temperature, IE running.
If your intake valve is not closing, it is unlikely that you have much, if any, compression in that cylinder. And that cylinder may not be running/heating. Either test method (performed properly) is going to find gross errors in cylinder function.

The leakdown test requires an air compressor and positioning/holding the crank at TDC You will be able to hear where pressure losses occur.

Either test should discover a valve that is not seating.

pinnacle · « **Reply #21 on:** November 22, 2009, 12:36:35 AM »

hello TT i 'll have to wait till monday to bring compression tester and leak down tester home from work i work at an auto dealer and have access to the equipment as i work in their shop. I was putsing around the bike today and ran it for a brief period and noticed another odd piece to the puzzle upon shutting down the bike i noticed what appeared to be white smoke floating out from the carb is this normal to occur and i just never noticed before or just another sign of something wrong in the combustion chamber? and i took a laser thermometer to the head pipes and according to it they are heating up fairly evenly also does that say anything to you....i realize until i get compression numbers you would just be speculating but even your speculations are valued and informative thanx...

TwoTired · « **Reply #22 on:** November 22, 2009, 01:41:32 AM »

I expect the white smoke is vaporized fuel...probably.

Even head pipe heat is a good sign. What RPM are you turning when you measure? Are you measuring the same distance from the exhaust port on each pipe? What is the spot size for your laser thermo? (It's not the laser spot size, btw. That dot is just the center of the spot being measured, often about 3/4 to 7/8 inch. Laser thermometer design and quality varies among vendors, like most any tool.)

pinnacle · « **Reply #23 on:** November 23, 2009, 05:13:15 PM »

alright T.T and anyone who wants to offer up some course of action .I brought home a compression tester and did the test as described and here are the results 150 psi on #1,145 psi #2, 65 psi #3,155 psi #4 cylinders. so number 3 has problem.hooked up leak down tester to it and it leaked like open tap through intake valve blowing straight through the carb. so obviously my intake valve has an issue. what do you suggest as my next course of action obviously the head has to come off again. but how do i distinguish between a bent valve or just a poorly sealing one and is it something that lapping the valve would cure as i don't want to touch the rest of the cylinders with them having good compression numbers. when i9 pulled the plugs 1,2,4 were very sutty any advise there could it be a result of no air filter and not being tuned properly yet.

TwoTired · « **Reply #24 on:** November 23, 2009, 05:53:52 PM »

The intake valve is probably bent. But, even if it isn't, you still have to look at the valve face and seat, which means removing the valve. You'll probably be able to look at each face and determine where the contact area is/or isn't from the residue on the faces.

The problem of bending the valve stem is the risk of damaging the guide during valve removal. If you are inexperienced, taking it to a shop might be a better choice and cheaper in the long run,(or get another used head/valve assembly to put on it).

Tune the carbs after the compression issues are repaired, and do have an air filter on it. Filters can change the mixture ratio.

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Author Topic: i need help with carbs please (Read 3299 times)