Topic: Engine diagnosis help please! <Solved>

[spanners]

Thank you!
I'm wondering if this will do the job?
It's around $30 with a coupon that I have.
https://www.harborfreight.com/air-tools/air-compressors/3-gal-13-hp-100-psi-oilless-pancake-air-compressor-61615.html
I've heard some people say to stay away from "oilless" compressors, so should I go with $100 ones?
I'm such a noob

Another option I'm considering is a simple air tank that can be refilled at gas stations etc.

Forget the gas station idea.
Oil less compressors are certainly noisier than oil filled ones, but that may or may not matter to you.  They certainly won't have such a long life, but it's horses for courses. 
If you are only blowing out carbs or using the air flow for cleaning bike parts or the odd blow your tyres up oil less are fine. 
It really depends on what you are going to use it for.  The one you mention has a very low CFM (how much air flow it can supply per minute from the compressor ) so expect to wait a while for it to fill the tank back up if you are blowing out full pressure using a lot of air from it.
It does have a regulator for the outgoing air pressure which is good, so although it does 100 psi, you can reduce down the output pressure which is handy for light applications. 

At the end of the day you get what you pay for,  (and I don't know how they do that for that price),  but if it is for light occasional use, and you are not planning on running any tools off it, and if you don't mind waiting 4-5  min for it to reach 100 psi,  I can't argue against it. 

The one I have https://www.sgs-engineering.com/air-compressors/sc6h-6-litre-oil-less-air-compressor  (an English web site but a lot of info on there as a guide to buying)   Which is a lot more expensive, actually has a smaller 6 Litre (1.3 Gallon)  tank but a much higher CFM of 5.7  It takes only about 90 sec to 2 min to fill the tank from zero pressure, but once up to pressure copes quite well with topping up.  Even this would not be any good for powering tools other than staple guns.  I have the flexy spiral air pipe on mine and a selection of low cost small short tube shaped nozzle attachments of different sizes off ebay.   Hope that helps.

[jgger]

Spanners is right, that compressor is OK for blowing off parts..........that is about it. The CFM  and  horse power are the 2 things you want to look at. Also you probably want something that rubs on 110 not 220.

To get an idea of what you want look at the CFM requirements of some common air tools. You will see that that HF model will work for balloons and bicycles.

[SOHCiro]

That was very informative and educational!
I don't plan on using power tools with the air compressor,
The purpose will be more for just leak down test and occasionally blowing carbs.
Thanks

[SOHCiro]

After doing some researches, I'm quite hesitant on removing the engine off the frame just to change the valves and rings..
My garage has no doors, and is occupied by my roommates and my car. I also don't have the space to store a lot of large parts in the apartment:(
I think i'll cut the 2 top tubes, and get one of those frame kits down the road.
Although structural integrity is another story, I plan on keeping the bike for a long time, so I'm not very worried about depreciated value from modified frame 

[spanners]

After doing some researches, I'm quite hesitant on removing the engine off the frame just to change the valves and rings..
My garage has no doors, and is occupied by my roommates and my car. I also don't have the space to store a lot of large parts in the apartment:(
I think i'll cut the 2 top tubes, and get one of those frame kits down the road.
Although structural integrity is another story, I plan on keeping the bike for a long time, so I'm not very worried about depreciated value from modified frame 

eek       don't cut the frame, don't assume its valves yet when you have one plug black and the others clean as a whistle !!

[SOHCiro]

Haha ok!
I'm going to get some sea-foam down the #2 intake.
If I'm lucky, and if it's a stuck valve, that may solve the problem!

I've just checked secondary circuit resistance, it read 24k ohms, so it should be fine.

[spanners]

Sorry.... don't know what others think out there?  anybody?  but I would personally not do that either (sea foam that is) unless you are 100% sure you have a valve problem to start with and nothing to lose by trying it.   

If you don't have a valve problem you might create one, because you are going to loosen a shed load of loose crap who's only way out is through the exhaust valve.  So some at some point for sure some of it will get hammered between the valve and seat.

If you decide to do that anyway, you want to re check that cylinder valve clearances after you have done it and before you ride it again in case the clearance has reduced.   Cut the frame... sea foam.. I need a lie down now after that stress  lol

[SOHCiro]

Update:
Seafoam didn’t exactly work.
I let it run at 3k rpm while dumping sea foam into the carb vacuum screw, made a smoke show, and let it sit for 20mins.
Took it out on the highway, it reved beautifully until 7k rpm in 5th, then bogged down again. Same symptom, now slightly worse. Power loss at 4k rpm.
Should have listened but I had to try! 
I’ll check the valve clearances once again.

Is there an individual Keihin Carburetor that directly replaces just the #2 carb?
It’s the round top carb, says “064A” on top of #4 carb.

[SOHCiro]

So... I'm not sure if anybody's still interested in this topic, but I think I've figured out the problem!

My symptoms exactly match burnt/broken exhaust valves.
What verified it was the suction from exhaust tip, using thin paper method. Idle popping is also getting more obvious and consistent.
Moving the advancer nut behind the points cover through #2 compression stroke has become unbelievably easy too.

I'm determined to re-lap valves, and replace rings.
I have one last question to ask to my wonderful friends on this forum.
With the top rail tubes cut, how much space will I gain exactly??
Does the head come off, so that I can replace the base gasket as well?

Thank you!!

When this goes all well, I'm planning to host a group ride. I am located in California, bay area.
I'm going to Japan to visit my relatives this summer, so give me a heads up if you need help getting some cool parts at local price, though they have to be reasonably light to be put in my luggage

[rickman750]

With the top rail tubes cut, how much space will I gain exactly??
Does the head come off, so that I can replace the base gasket as well?

With the 754's weldless frame kit, the entire top end can be removed.
My K2 top end is in the process of going back together after replacing the studs to fix an oil leak. I'm taking the opportunity to switch to floating rocker pivots as well. (Thanks for your help, Hondaman!)

[PeWe]

With the top rail tubes cut, how much space will I gain exactly??
Does the head come off, so that I can replace the base gasket as well?

With the 754's weldless frame kit, the entire top end can be removed.
My K2 top end is in the process of going back together after replacing the studs to fix an oil leak. I'm taking the opportunity to switch to floating rocker pivots as well. (Thanks for your help, Hondaman!)

No problem to lift cylinder off too!
Then much easier to pull the rest of engine with a strap. One man job.

[spanners]

So... I'm not sure if anybody's still interested in this topic, but I think I've figured out the problem!

My symptoms exactly match burnt/broken exhaust valves.
What verified it was the suction from exhaust tip, using thin paper method. Idle popping is also getting more obvious and consistent.
Moving the advancer nut behind the points cover through #2 compression stroke has become unbelievably easy too.

I'm determined to re-lap valves, and replace rings.

So earlier in the thread you said,
''Checked the compression dry.
Results are:
#1 -- 79psi
#2 -- 80psi
#3 -- 80psi
#4 -- 75psi''

Ignoring the fact they are (were) all a lot lower than they should be for the moment, If # 2 exhaust valve is guttered or not sealing, why is the compression similar to the others?  which don't have black plugs. 

Are you going to cut the frame and pull the head off on the basis of the paper test and the fact by hand it seems easier 'than before' to turn over through tdc #2  with a spanner?   
 
Is it possible, after squirting the sea foam in,  is it only now  lacking compression on #2. 
Have you done the compression test again?
Did you check the valve clearances again?
I think you are on a mission to change the valves whatever, and you might be right, just be 100% sure you are not missing a carb problem, that's all I'm saying.  With the bike apart your tests are limited somewhat.
 

[SOHCiro]

PeWe & Rickman750 -
Thanks for the info! Much appreciated

Spanners-
Yes, I fully agree that the compression reading doesn’t make a whole lot of sense...
Perhaps it’s the compression gauge I’m using. During the compression test, the pressure reading only gets higher and higher and stops after multiple cranks, unless I press the release button. In other words, it would read the highest instant compression value, even if it leaks and drops the moment after.

Going through the TDC cycles, it didn’t get easy just now, but rather progressive, and slowly over the past 3~4 weeks since the problem appeared. I’ve turned that thing so many times to figure out if it’s valve issue, timing issue, or whatever. :\

Another thing is I think the valves had already been burnt when I first got the bike and it’s getting worse.. I remember several times when I attempted to Vacuum sync the carbs, #2 carb had WAY higher vacuum than the rest, and could’t balance the carbs no matter how much adjustments I’ve made.
The mixture screws were cleaned as well, and now I see clear that failing valve was the cause.

The valve clearance so far remained the same since the last setting. It also feels odd that #2 tappet arm wont produce the clicking sound when I press it in the compression stroke. There’s certainly clearance, but feels like something is at the bottom, preventing it from fully seating. I haven’t looked at the inside, but for sure there’s something wrong.

Afterall, I wouldn’t be surprised if there is a carburetor problem too. But like you said I think it’s worth rebuilding the top end anyway. Once I know the compression is good, I’d be able to tell indeed if I need to work on the carbs again.  It’s a game of elimination I’ve learnt
 I really want to thank you for sticking by this thread and guiding me through all the possibilities! I would certainly not have made this much progress just by guessing on my own!!

[TwoTired]

Were it me, I'd find (or build) a leak down tester before I took the engine mechanical apart.

This will tell much more about engine mechanical health.  If you are leaking compression, you can also determine where it is leaking.

Cheers,

[spanners]

100% agree with that

[spanners]

So... I'm not sure if anybody's still interested in this topic, but I think I've figured out the problem!

My symptoms exactly match burnt/broken exhaust valves.
What verified it was the suction from exhaust tip, using thin paper method. Idle popping is also getting more obvious and consistent.
Moving the advancer nut behind the points cover through #2 compression stroke has become unbelievably easy too.

I'm determined to re-lap valves, and replace rings.

So earlier in the thread you said,
''Checked the compression dry.
Results are:
#1 -- 79psi
#2 -- 80psi
#3 -- 80psi
#4 -- 75psi''

Hi there,   I know you had the throttle open but when you took those readings did you have the choke on by any chance?    - the choke should not be on. 

In an old link in a different forum somebody got near identical readings to yours, because they tested with the choke on.  Other than your gauge very inaccurate or all cylinders down on pressure by the same amount, I'm trying to explain your lower readings.  Because nothing makes sense so far. 

Otherwise check your gauge against a known 100psi air line or buy that air compressor and check it against that. 

You also mentioned that when you put your carb sync gauges on,  #2  was really high!  may be I'm wrong here, but to me this does not suggest a valve problem.  I would have thought with a bad or sticking valve you would get a low vacuum or fluctuating pulsing normal to low reading ?   

[TwoTired]

I'm trying to explain your lower readings.  Because nothing makes sense so far. 

In the engine FAQ it explains that using a car or truck compression tester, it can add volume to the compression chamber  via the hose, and alter the compression ratio.

 If the chamber is 10cc and you add another 10cc to it, you get less compression from the same swept area of the piston.

Cheers,

[spanners]

Yes I can understand that, and, if that is the reason here, it would explain why they are all similarly low, but still does not point to a particular problem with #2  compression.  SOHCiro is convinced this is an #2  exhaust valve problem. 
 
Either way hopefully you have enough info to work it out now SOHCiro one way or the other,

[SOHCiro]

Hello gents,
It's been a while and I finally got my bike to run perfectly! 

After my last post, I did a budget-ish top end rebuild. I've changed the rings and gaskets, honed cylinders, and lapped/replaced valves.
Oil filter was replaced as well and the bottom oil pan was cleaned.
Put them all back together, the mysterious rough idle popping was gone , but the high rpm hesitation still remained.

In addition, it also started misfiring during idle. What I mean is, I could clearly tell by the sound, sluggish rev, and the loss of power that it was running on 2 cylinders. It was unstable, like it would run on 2 cylinders for 10 seconds and all 4 would fire for 5 seconds and repeat kind of thing.
Weirdly, all 4 plugs looked equally black, and 2-3 pipes were relatively colder than 1-4, which made me think about ignition problems again.

Looked at wire connection once again, tested fuel flow, float level, valve gap, timing, ignition, battery voltage, you name it.

Today, I had it idle with my points cover off and started wiggling with the connection in the points assembly.
What I've always overlooked was that one of the condensers had an "inflated" black rubber tip.
I played with it and decided to push the rubber tip back into the metal housing with a screw driver, and voila!
Extremely bad-smelling gas spewed out of the condenser  , and suddenly all 4 cylinders fired up and I knew the problem simply disappeared.
It's weird because the condensers are both 3 months old and the inflation must have happened overnight.
JFYI I got them from 4into1. I love the site and I don't mean to diss their reps. I've ordered hundreds of dollars worth of parts from them and 99% of the parts I got work flawlessly.

This was a long battle and such a great learning experience, I'm sure it will continue to be.
I feel dumb to have spent almost 2 months chasing this tiny problem, but I hope I gave you guys a good laugh at the end!
Thank you again for all the help, and I sincerely hope this post will help my fellow riders in the future.