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Author Topic: Ignition or carb issue?? Full choke only  (Read 671 times)

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Offline nixon

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Re: Ignition or carb issue?? Full choke only
« Reply #25 on: October 22, 2018, 06:27:18 pm »
  Make sure you have not got any fouled spark plugs.
Ok thanks... they were new nhk  when I tried to figure this out. So I've run 5 min on rich with choke.  Should I replace or clean?

Offline TwoTired

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Re: Ignition or carb issue?? Full choke only
« Reply #26 on: October 22, 2018, 08:30:42 pm »
If the center electrode insulator isn't coated with black conductive carbon, the plugs should fire properly.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Thinking:  It's like reading with your own mind

Offline nixon

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Re: Ignition or carb issue?? Full choke only
« Reply #27 on: November 08, 2018, 01:20:38 am »
Ok back , kinda to square one.

I installed some new solid core copper leads with ngk 5phm caps..hoping slight or drastic change. Nothing. still only ran full choke. if reduced choke or could just get idling , barely.


Convinced its carbs, i wound in air screws..all the way. Fired up fine, all cylinders..and pretty soon i could wind on throttle getting to rev quite high, then return to idle. no choke required.

Ive rigged a funnel into fuel hose as painting tank, and 8pm so didnt want to annoy neighbours too much..

but please, any input on what i should do or try next.. ..needle... jets , main, slow...is that ok to ride with air screws closed? whats going on.. still a newbie with carbs!!

Offline TwoTired

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Re: Ignition or carb issue?? Full choke only
« Reply #28 on: November 08, 2018, 08:07:30 am »
What do the spark plug deposits tell you about combustion conditions?

Are all the head pipes equally hot?

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Thinking:  It's like reading with your own mind

Offline nixon

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Re: Ignition or carb issue?? Full choke only
« Reply #29 on: November 08, 2018, 11:37:58 pm »
I'll clean them and see how it looks tomorrow.  No real issue having air screws completely closed? That says running lean on slow jet?

Offline TwoTired

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Re: Ignition or carb issue?? Full choke only
« Reply #30 on: November 09, 2018, 08:20:41 am »
I'll clean them and see how it looks tomorrow.
Cleaning off the deposits on the plugs removes the evidence about how the cylinders are combusting.  Information you want. Like is it running rich or lean or the same among the cylinders?

No real issue having air screws completely closed? That says running lean on slow jet?
The issue is, it is not in anyway normal.  That would concern me and lead me to investigate why.
Remove one of the pilot screws.  Is the tip hollow with a cross drill?  If so, you can't really turn the circuit off with that screw.  You can only set it to minimum by design.  Normally, by design, your off idle response under load will make the engine stumble with the screws all the way seated.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Thinking:  It's like reading with your own mind

Offline nixon

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Re: Ignition or carb issue?? Full choke only
« Reply #31 on: November 09, 2018, 04:31:54 pm »
appreciate your input!

They were black sooty , dry before i cleaned. Cleaned up easily. I thought to  clean , as id only had it running with full choke?

so thought clean and see again how they looked now that i can run without using  choke .

I should have mentioned - its idling , revving but hanging a little - with no choke now..but only with the rubber velicity stacks. And air screws completely closed.

If I add the unifoam filters over the stacks , I cant get running. Choke or no choke. Unscrewing the screws 1/2, 1, 1.5,2 made no big difference.


Offline nixon

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Re: Ignition or carb issue?? Full choke only
« Reply #32 on: November 09, 2018, 04:46:16 pm »

[/quote]
The issue is, it is not in anyway normal.  That would concern me and lead me to investigate why.
Remove one of the pilot screws.  Is the tip hollow with a cross drill?  If so, you can't really turn the circuit off with that screw.  You can only set it to minimum by design.  Normally, by design, your off idle response under load will make the engine stumble with the screws all the way seated.

Cheers,
[/quote]
yes it does have hollow tip with cross drill.  And 100% yes stumble with the air screws closed. if im very gentle i can get it to rev more. But it was idling ok and that for me is a big deal! Pretty sad huh..

All headers equally hot , tested with water spray 

Offline nixon

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Re: Ignition or carb issue?? Full choke only
« Reply #33 on: November 09, 2018, 05:27:36 pm »
Which of the following should I be checking, adjusting? what could cause it to run with air screws closed - no filters over stacks, but wont run with turnred out screws when foam filters over stacks?

- Main jet ?
-idle jet?
-needle height?
-float heights
- ( other reason, im open to checking rechecking anything - havent ridden this bike for 3+ months!  )

Has brand new oem honda intake rubbers to engine.

When i pulled plugs 1 and 4 after cleaning - 1 was dry sooty and 4 was much cleaner?
« Last Edit: November 09, 2018, 05:59:10 pm by nixon »

Offline TwoTired

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Re: Ignition or carb issue?? Full choke only
« Reply #34 on: November 09, 2018, 08:38:21 pm »
If the float bowl fuel level is too high, it will bleed extra fuel into the intake runners.  At any rate, all the carb metering components rely on a known good float bowl fuel level to be consistent in metering.
If the float components are still stock, probably can be confident with a float swing measurement.  If the components aren't originals, then the clear tube method for actual fuel level verification is recommended.

That's where I would start.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Thinking:  It's like reading with your own mind

Offline nixon

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Re: Ignition or carb issue?? Full choke only
« Reply #35 on: November 10, 2018, 12:43:55 am »
Thanks! I'll pull the carbs and assess.

Offline nixon

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Re: Ignition or carb issue?? Full choke only
« Reply #36 on: November 10, 2018, 05:01:34 pm »
If the float bowl fuel level is too high, it will bleed extra fuel into the intake runners.  At any rate, all the carb metering components rely on a known good float bowl fuel level to be consistent in metering.
If the float components are still stock, probably can be confident with a float swing measurement.  If the components aren't originals, then the clear tube method for actual fuel level verification is recommended.

That's where I would start.

Cheers,

Twotired, I owe you a beer or 5!!  I had one original brass float, 3 black plastic ones. Only one was on 26mm! one was out 3mm.  I found another plastic one,  and carefully set them all.

Now - with foam filters on..i could run with no choke..and it revved quite cleanly within a few minutes! I started adjusting air screws.. 1/2 turn seemed ok but ill adjust according..back out till stumbles then 1/4 turn in?


From here I really need to take it for a ride and see whats happening WOT etc once warm ... thanks for listening to my rambles ppl!




Offline TwoTired

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Re: Ignition or carb issue?? Full choke only
« Reply #37 on: November 10, 2018, 06:41:21 pm »
The early fours all normally ran a bit rich in the idle regime.  Part of this reason is because the carb had no accelerator pump with the mechanically actuated slides.
When the slide is raised from idle, the carb throat vacuum rapidly falls.  The throat vacuum is what draws fuel from the jets. Low vacuum = low flow.  So, the mixture goes lean and if the vacuum is allowed to fall too drastically, the mixture ratio goes too lean to even fire in the chamber.  This stumble or wheeze as I like to call it, is immediately corrected by backing off on the throttle, and the engine resumes operating cleanly as if it was just switched on.

With these carbs, you should never expect the engine to respond well to whacking the throttle wide open from idle position, with or without load.

My method for pilot air screw adjustment:
Mark your throttle with some temporary tape.  So you can tell at a glance what the 1/2 applied position is.
While the bike is moving, put it in top gear and have the engine operating at about 1000-1500 in cruise. Suddenly open the throttle to the 1/2 point. If it wheezes, you need to make the pilot screws richer.  If it takes throttle and slowly increases speed you have an over rich idle.  If you can give even more than 1/2 throttle and the engine picks up predictably, the idle is too rich, and prolonged idle will carbon up the plug insulators, which causes a whole other set of issues.  So, make sure your plugs are clean before starting this test.  Anyway, if you can give it more than 1/2 throttle with reliable pick up then the pilots screws need to leaned out until the test passes with 1/2 throttle travel and no more.

I'll admit, I never tried this method with velocity stacks, as I hate them on a street bike (fine for full race at the track).  But, this tuning makes for a predictable and long lasting state of tune for the pilot air screws and the spark plugs.

Of course the slide needle and main jet have their own procedure for fine tuning.

Cheers,


Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Thinking:  It's like reading with your own mind

Offline nixon

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Re: Ignition or carb issue?? Full choke only
« Reply #38 on: November 11, 2018, 12:03:59 am »
wow thanks for your input! really appreciate it.

I wasnt sure a stock air box will fit the auto version with round top carbs, so ( stupidly it now seems) I took easiest route with ram air filters over stacks. i should mention i have only the one arm so fiddly jobs i put off!

i have installed bungs in the 4 into 2 headers a o2 sensor so im gonna take it to a mate whose a great mechanic now i can hopefully ride it there

 

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