Topic: Engine diagnosis help please! <Solved>

[SOHCiro]

Sorry, what exactly do you mean by the other end in same coil?
The black&white wire from the coil?

Thank you

[Deltarider]

You might as well forget about it. I just reread what you posted above and I see you have already tested the #2 cap. To answer your question now: you've shown you're able to test the primary resistance. The secundary circuit is tested by pulling the plugcaps from the plugs and then have one probe in cap #2 and the other in cap #3. The secundary resistance inside the coil usually is 13 - 15 kΩ. An individual cap's resistance should not be over 8 kΩ. So with the plugcaps connected to their wires, total resistance should not be over (15 + 8 + 8  = 31 kΩ. If it is, plugcaps should be unscrewed from their wires for individual measuring. BTW, can you recall what the last thing was you did, before the problem began?

[SOHCiro]

I see.
I've been working on the bike almost everyday for about 3 months, and I can't exactly recall everything I did in perfect orders

But what I remember is, I replaced the entire electrical harness with LED lights, replaced condensers, then replaced petcock.
Shortly after, bike ran like crap, did valve lash, points&timing, then eventually found that all 4 main jets had dropped to the bowl!

I put them back on tight, ran good for a few days, and the problem began.
I looked at everything again, found cracks in the main jet post, on carb #1 and #4, probably due to over-tightnening it.
I wasn't sure how long it had been like that, but I sent the carbs for laser-welding, the crack is completely sealed now.
I pulled the carbs out and soaked them in carb cleaner, blew air and thin wires through passages.
The emulsion tube was a little bent, so I hammered it straight and put it in #1 carb.
I checked and all the needles seem straight, and I can't find any flaws in the carbs, except for the weird float height problem.

Since #2 plug is black, I don't think the crack had anything to do with the problem though...

[SOHCiro]

Is 2+3 points small arcing normal?

[Deltarider]

No. Compare it to the vid shown in my first reply. A bit of sparking is normal like shown in the vid at (2+3), the arcing at (1+4) however indicates a faulty condensor. Another cause could be that after you fitted the breakerpoints and/or condensers, one of the forked terminals at the back of the breakerpoints is too close to the plate and so intermittently makes contact to ground. The 2+3 breakerpoints is more prone to this, because it's more in the vicinity of plate and crosshead screw than the 1+4 breakerpoints. Make sure the forked terminals don't touch the plate!

[SOHCiro]

Cool, just wanted to double check!
On mine, 1+4 points have no arc at all, though 2+3 spark exactly like the one in the video.

[SOHCiro]

Spanners-
Yes, the engine hesitate to accelerate under load. In neutral gear it is unnoticeable.
in 1st and 2nd, it only hesitates to accelerate at around 7- 8k rpm so I don’t really have problems in regular city riding.
However, on the highway in 4th and 5th around 5k rpm, it gets worse at relatively lower rpms.
I’m not a 100%sure what “misfire” sounds like, but I can tell that there is significant power loss, and the exhaust note is different and uneven. it sounds like the engine is  gurgling, and backfires.

I think the pop occurs at the end of exhaust section, which makes me believe that one cylinder misfires — left over mixture ignites with the hot exhaust pipe.

My helmet cam recorder is useless when it comes to sound recording on windy highway, but I’ll see if I can record the noise with my phone and edit it together with the video.

I have yet to remove the points plate assembly. What should be taken into considerations when looking at the mechanism behind the plate?
Thank you!

[spanners]

Misfire been a pretty obvious erratic burble where it suddenly sound like a cylinder or more is firing/not firing with sudden loss of power.

As the engine speed increases the trigger to fire the sparks has to be sent out much sooner,  or it arrives to late past TDC and you lose power and overheat valves.
http://forums.sohc4.net/index.php?topic=131339.0   the springs are normally supposed to be pretty loose on these but if one is broken the timing will advance to soon, if the mechanism is tight it will not advance enough or at all.

It is more difficult for a plug to fire under higher compression load than lower,  so if you don't have a problem at 7 - 8K 1st 2nd gear I don't think an electrical problem or advance retard problem.   

It's also more difficult to ignite an over lean  mixture to burn completely. Looking at all the work mentioned relating to the carbs and the colouring of the plugs I wonder if this is still some sort of fuel starvation related problem and not electrical.  Bad timing can cause popping in the exhaust or inlet manifold, but so can a fuel problem.

Out of interest, why did you change the petcock?  was it not sealing?  did you put a new one on then or re sealed second hand one ?
a bent emulsion tube sounds a bit ominous was that in n2  do you remember?

[Deltarider]

I have yet to remove the points plate assembly. What should be taken into considerations when looking at the mechanism behind the plate?

Why do you have to? Proper functioning of the advancer can be tested with a stroboscopic light. If you don't have one and have the advancer out, check it for smooth movement.

a bent emulsion tube sounds a bit ominous was that in n2  do you remember?

+1. Could it cause the needle to stick?

[SOHCiro]

The petcock was replaced due to leaking.
It seems like I’ve overtightened all 4 main jets, but only carb 1 and 4 had cracks in the tower.
#2 carb jet tower looks slightly bent at the tip.
There is a straight emulsion tube in there, and it feels like a good fit though.
But who knows, maybe it’s not sealing and there is gas leaking into the cylinder and making the mixture rich...
Gas flow to the carbs are good. With the bowls are off and manually moving the float up and down, gas flows out really well, uniformly across all 4 valves.

[Deltarider]

If the fuel metering (main jet, needle jet) for whatever reason is not sealed well, the cylinder's vacuum will greedily suck in the extra fuel.

[spanners]

If the fuel metering (main jet, needle jet) for whatever reason is not sealed well, the cylinder's vacuum will greedily suck in the extra fuel.

Deltarider is spot on here,  double check this,  there is not a lot of distance down in the bore for the o ring to seal the jet, it does not take a lot to cause a problem that can also easily be temperature related.  Assume we are talking about the same area circled in green below.  This is from CB550 1975

[SOHCiro]

Yes! That green circled area is slightly "crushed" at the tip, rather than "bent".
I've just put 2 o-rings over the threads, will see how it runs when I take it out in a few hours.
I'm still not sure why it pops in idle though, I'm running 40 pilot, 120 main. I've tried 110 main, it felt a little lean.
Maybe a larger pilot will cure the popping?
It has stock 4-1 headers and aftermarket cone muffler with no baffles or packing in it.
I bought it with no airbox, so running clean individual pods.
I'm fully aware that stock airbox defeats everything One day if a good deal comes up i'll get it

[scottly]

I'm still not sure why it pops in idle though

The popping may be un-burnt fuel from the excessively rich #2 cylinder igniting in the 4-1 pipe from the fire from the other three cylinders.

[SOHCiro]

Update:
O-rings in the carb didn’t work...
I’m running 40 pilot jet, idle smells rich.
1,2, and 3 plugs look white and 2 looks black.
Does this indicate bad exhaust valve?

[American Locomotive]

Just to verify some things about your compression test:
- You did the test wide open, correct?
- Let the engine crank through several compression cycles (at least 4-5)?
- Your compression tester is a proper unit, with a check-valve located in the tip that screws into the motor, correct?

If so, 75-80 PSI compression is extremely low. That's the cranking compression my CRF450R has - and that bike has an automatic compression relief that literally lifts the exhaust valves halfway through the compression stroke. I have flathead lawnmowers with 5:1 compression that will compression test around that amount.

You may want to consider doing a leak-down test.

[Deltarider]

Cool, just wanted to double check!
On mine, 1+4 points have no arc at all, though 2+3 spark exactly like the one in the video.

Just to make sure: if by 'though 2+3 spark exactly like the one in the video' you mean like 2+3 in the video, there is no problem, but if by 'though 2+3 spark exactly like the one in the video' you mean like 1+4 in the video, there is a problem.

[SOHCiro]

American Locomotive-
Yes, tested with throttle wide open, several cranks, brand new tester from harbor freight 
I've been wanting to do a leak-down test, but have no access to an air compressor...

Deltarider-
I meant, 1+4 has no sparks, 2+3 sparks a little bit.

[Deltarider]

OK.

[SOHCiro]

What are the things to keep in mind when changing the exhaust valves myself?
I'm also planning to replace rings to re-gain as much compression as possible.
With more than 50,000 miles on the motor, I don't think it has ever been open!!

I'm assuming it's not as simple as taking the old ones out and putting new ones in.
Do they have to be professionally ground and lapped?
I have new guide seals and all the gasket parts being shipped right now as well.

And is it really worth the cost to get a decent air compressor?

Thank you

[dave500]

you can lap the valves in your self with grinding paste,any cheap direct drive air compressor will work for your needs,belt drives are much quieter but get expensive.

[SOHCiro]

Good to know!
I'm also wondering what "valve-shims" are for?
I keep seeing them and I guess they use it for worn out valves?
Do I need them even if I'm replacing the valve with a new one?

[dave500]

you don't need shims,later bikes use a shim you place on the valve stem to adjust the tappet clearance,your bike has an adjustable screw and lock nut type.

[spanners]

What are the things to keep in mind when changing the exhaust valves myself?
I'm also planning to replace rings to re-gain as much compression as possible.
With more than 50,000 miles on the motor, I don't think it has ever been open!!

I'm assuming it's not as simple as taking the old ones out and putting new ones in.
Do they have to be professionally ground and lapped?
I have new guide seals and all the gasket parts being shipped right now as well.

And is it really worth the cost to get a decent air compressor?

Thank you

There are many things to consider when pulling an old engine head off.  Do you replace the cam chain?,  I would,  chain tensioner certainly, check valve guide wear, check the bores for size and  get the bores honed  so that the new rings seat properly.  You need to spend a lot of bedtime reading on this one first I think  . 
A small low cost compressor was one of the most useful tools I have purchased.  Wished I had got one sooner once I had it.  I have the oil free type.  Which for the light duty I use it for is fine. 

Also have you not got a carb synch tool?  you can tell a lot from sticking one of those on.  I know the good ones are not low cost, but if you are working on 4 cylinder bike engines I would consider it essential.

[SOHCiro]

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.