Topic: clogged jet?

[3ntr0py]

hello all.
on my last ride i noticed that three of my pipes, #'s 2-4 (assuming that the pipes are numbered left to right while sitting on the bike) were turning a nice shiny gold color that i haven't seen since i've owned the bike. my LIMITED knowledge told me that probably meant that they were running hotter than #1, and sure enough i did a touch test and the #2-4 pipes were nice and hot and my #1 pipe wasn't. it was very warm, but i could pretty much grab it while running. doing a bit of research on this site i found a couple threads that mentioned that this could be caused by a clogged jet. keep in mind that i have absolutely zero experience working with carbs. i'm sure i'll get there, but i haven't been an SOHC owner for long. anyway, my question for everyone is, is a clogged jet usually the culprit when one pipe is running cooler? if so, how easy is it to check/fix for someone with little experience?

bike info:
1975 CB550F Super Sport
stock 4 into 1
carbs rebuilt about a year and a half ago (done by PO)

let me know if any other specific info would be helpful.

thanks in advance.

[Buffo]

first make sure you have spark to that cylinder and check the plug for type of deposits

[scondon]

      I'll second that Buffo. I've had the "warm pipe" syndrome and it was caused by weak spark. Either a faulty plug cap or rusty wiring at the tip of the plug lead. Switch your 1&4 plug leads and see if the problem follows. There are other things that could cause your symptom, but this is the easiest one to check.

       A partially clogged jet will cause that cylinder to run much leaner/hotter, either at idle or at running speed depending on which jet is clogged.. A fully clogged jet will make the bike run like utter crap.

[GroovieGhoulie]

I'm having a similar issue with my bike.  I'm trying the fuel route and the electrical route.  However, the plug was a nice tan color, so it didn't look too rich or lean.

[Buffo]

it could be running really rich and fouling the plug...

Check for spark first, with new plugs, make sure you gap them properly...then, if you have an GOOD, CLEAN spark, replace all of your plugs, do a plug chop at the proper throttle settings...

Buffo

[TwoTired]

1. how do i check for a good clean spark?

Remove the spark plug, insert it into the ignition lead, and lay the body onto the cylinder block.  Crank or start the engine.  Ignore the noise and debris coming from the open spark plug hole, but don't let it spit in your eye, either.  Do observe the center electrode has a spark that jumps the spark gap.  Note the color.  Blue is very attractive, orange is nice.  But, I'd rather see blue.

2. what is the proper plug gap for the 550?

About  .022 to .025 inch

3. how do i do a plug chop and how do i make sure to do it at the proper throttle settings?

Before I did the plug chop thing, I would pull all the spark plugs, keeping the cylinder orientation, and compare them to the pics at:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
  All the plugs should have the same deposit type.  If not, you have to locate why.
Tell us what you find.

Have you checked your plug caps for 5K -10K resistance?  And verified they are screwed firmly onto the ignition leads?

Did you drain and catch the contents of each carb float bowl, looking for contaminants?

Cheers,

[Briboy]

Hi
My cb750 might have the same prpblem,the last time I rode it no problems 5 weeks later the problem started,when starting 2 pipes get hot and two are cold,and sometimes backfire,any ideas.
briboy.

[TwoTired]

follow up:
i just pulled the #1 plug and did a spark check. it appears to be good (as far as i can tell). it was MOSTLY blue with occasional sparks of orange in there. i also drained the #1 carb and there were a few TINY specs of something in there, but nothing that really jumped out at me.

Your spark is probably good enough.  The plug may be starting to carbon foul and bleed off some spark energy. 

There are still several possibilities.
How old are those plugs?
What is their number?
Do the black deposits feel dry powdery or oily sticky?
You still running the stock air filter?

Does the black spot on #4 scrape off?  Or, has the porcelain glassified?  Describe that deposit.

Making some assumptions, I may regret later, the plugs seem to indicate the dark one is running richer than the others.  IF the compression is even across the cylinders and all the other items on the tuneup checklist are up to new and peak spec, I would guess there is an issue with No. 1 carb.

If it turns out to be the carb(s) here are some possibilities:
Carb Synchronization error
Pilot screw Air bleed setting different from others.
Wrong pilot screw installed in some of the carbs.  (some types are hollow, yours s/b solid)
slow jet damaged (enlarged from cleaning orifice with wrong tool)
Slow jet loose.
Main needle set at wrong or different height than other carbs.
Wrong main needle installed or different from other carbs.
Needle jet emulsion tube cross drilled holes clogged (or at least some of them).
Main jet oring leaking or carb body corroded to prevent proper seal of main jet.
Float height setting incorrect.
Float needle and/or seat leaking.
Float needle seat oring leaking.
Main or slow system air jet partially restricted.

When examining fuel drainage, specs larger than .016 inch can clog/block slow jets.  A blocked slow jet will frequently give you a cold head pipe and poor idle performance, as cylinders won't fire at all without fuel.  I suspect this is Briboy's issue.

Too much fuel (due to some leakage or setting error) in the fuel/air mixture can cool the combustion temps and head pipe, too.  Sooty carbon deposits on the spark plug insulators is evidence that the cylinder temps are not high enough to completely burn the fuel, leaving behind unburned hydrocarbon deposits (soot).  This is probably 3ntr0py's issue on #1.  Not sure about #4, yet.

Cheers,

[Buffo]

as you have a different bike with different carbs than I have I was hopeing TT would post a course of action.

[BobbyR]

Everyone gave you great suggestions here. I will give you one. DO NOT DO TOUCH TESTS ON THESE PIPES YOU CAN BURN YOURSELF FASTER THAN YOU WILL BELIEVE POSSIBLE. One test which has merit is to put a drop of oil on each pipe up near the flange. You can see which pipes are hotter than the others from the burn off time of each drop.

[dusterdude]

bobby,you just need to be quick.i do it all the time and i havent burned my old fingers yet.

[TwoTired]

the ones that are currently in there are D8EA's and i'm not sure how long they have been in there.the plugs i bought today are D7EA's. should i definately do a plug chop after i have installed the new plugs?

The D7EAs you bought are the correct ones.  Were it me, I'd save the plug chop for after I got all the cylinders running on equal mixtures.  Even then, your bike modifications are so slight, putting everything in the carbs back to factory settings will most likely solve remaining issues.

as for the air filter, the one that is in there is the one that the PO installed. it think it's a UNI filter. it's black foam instead of the standard paper filter. if it is a UNI filter, can't i take that out and clean it under water?

Uni Filters are what I use too.  They must be cleaned in a solvent and then re-oiled for proper effectiveness.  Uni sells spray cans of cleaner and the proper oil for that filter.

maybe it is running a bit rich beacuse of that? i don't know enough to say whether or not that could be the case.

Wishfull thinking, I'm afraid.  Perhaps a fuel starvation from a petcock problem.  But, too rich on one cylinder?  Hard to imagine a supportive senario.
Cheers,

[Bodain]

bobby,you just need to be quick.i do it all the time and i havent burned my old fingers yet.

I'm with you. The touch test is the absolute best test. It requires no extra accessories.
A bit of saliva on the finger. A millisecond touch... You hear the sizzle... The pipe is ON.
This is much like putting your finger quickly in a flame. No issues here.

Now anyone that grabs a handfull of pipe and holds it there checking for temp. Gets what they
deserve.

[Dennis]

so that's all i have now. i also pulled my air filter out and it didn't LOOK too dirty to me, but then again it is a black foam filter, so maybe i'm just not able to see the dirt/debris.

 

try running with out the filter (for test purposes only) if you think it could be too restrictive

[TwoTired]

D7EAs are hotter plugs than D8EA (meaning they maintain combustion chamber heat better than D8).  On all my CB550s this resulted in faster warmup and better running before and after warm up.  D8s made a standing warm up before riding mandatory.  Whereas with D7s, I can start and go, leaving a choke on while it warms up during riding.  Depending on temps the choke gradually gets moved toward off position until it will idle without the hand holding the throttle.  Six different CB550s behave in this way, leading me to believe it is characteristic of a properly running bike.

Have you finished the whole tuneup process yet?
Did you gap the plugs?

Have you pulled the plugs and verified that all the cylinders are now running about the same combustion conditions.

If so, then do as Dennis suggests amd take out the air filter for a rest run.  Check your bike response characteristics at different throttle settings.
Conversely, apply partial choke and repeat the throttle checks.  Does either test improve performance?

These checks are only going to be meaningfull if all the cylinders are running the same way.

What are your pilot screw settings?

Might help if you answered the questions asked in previous posts.  If you hide information from us, our help will be limited.

Cheers,

[damn_yankee]

I use a spray bottle to test the pipes. It is much safer. The water should sizzle off.
If one pipe is colder, pull the plug wire off and then push it back on. The bike should slow and pick up if it is firing (assuming you have spark and gas). I wear a rubber glove usually.
If it doesn't slow and then pick up the jet(s) are probably clogged or the pilot screw is closed.

Jeff

[TwoTired]

I use a spray bottle to test the pipes. It is much safer. The water should sizzle off.

Best to use distilled water for this method.  Or, you will have mineral deposits on your chrome pipes.

Steam burns can be just as painful contact burns.

I use the flash touch method for comparing head pipe temps.  It takes time to transfer heat into your fingers. There is also a time lag before you actually sense the feeling of heat.  Keep the contact time very short and you don't feel the heat until after you've removed you fingers.  Keep the contact time to too-short-to-feel.  Then gradually extend the short contact time until you can gauge the temp.  Other pipes ought to end up with about the same contact time/heat feel.  Start each pipe test with the assumption that it is way hot.  And, never as cool as the last one you touched.

Cheers,