Advice on starting after valve shim adjust. She's proving tough

[Guest]

Hello,

Since the bike has been running poorly I decided no harm in checking the valve shim clearance. Turns out everything was under spec and I actually had to borrow a 2.45mm shim and move it to 5 of the valves just to get a reading. I've now got all of the valves adjusted with clearances where I can either fit a 0.076 or 0.102mm feeler between each cam lobe, I think one just barely allows a 0.127 when at the proper position.

The last few times I've performed a bench sync on the carbs and then thrown it on the bike I've gotten it to fire up right away. This time, however, I haven't been able to get it to fire. I noticed there is a significant difference in how the engine cranks now with the choke fully on vs off. You can actually hear the difference. Really seems to be pulling air through a lot better than before. I can hear a difference out the exhaust pipes too when just cranking. I plugged in the Carbtune to take a look and there's a marked difference between choke and no choke on there as well. There's no boot leaks as they're all new. Bench sync was done and I've got nice spark on all 4 plugs. Just doesn't seem to want to fire.

I might try some quick start to see if that'll get it running and hopefully prime all the vacuum tubes but usually by this time I've at least had a cough out of it. (And before you ask, yes, carbs have been dipped twice this year with new o-rings. Floats triple checked, new OEM Suzuki petcock and everything else on the "my bike is running like a sack of crap" checklist. All but the final piece which was the valve shim adjust. It was running good at higher rpm till this point but struggled at low end and 2-3K).

Hope I can get some ideas and get back to it after work tomorrow.

Thanks

[Bortasqu]

You did rotate the engine to squeeze out all of the oil on the buckets before and after adjusting, yes?

[gs11ezrydr]

Sounds like to me you may need to recheck your valve clearances since these problems began after the initial adjustment. Do a compression test and a leak down test if you have the access to the proper equipment. This will tell you what is going on inside the engine. Eliminate these factors first.

[Steve]

The last few times I've performed a bench sync on the carbs and then thrown it on the bike I've gotten it to fire up right away. This time, however, I haven't been able to get it to fire.

It appears that it was running (although poorly?) before? Why did you remove the carbs to do a bench sync?

I plugged in the Carbtune to take a look and there's a marked difference between choke and no choke on there as well.

Just so you know, trying to get any meaningful Carbtune numbers while on "choke" is an exercise in futility. The purpose of the carb sync is to coordinate the opening of the throttle butterflies by balancing the vacuum readings. The "choke" bypasses the throttle butterflies, so any readings on the gauge are useless.

I might try some quick start to see if that'll get it running and hopefully prime all the vacuum tubes ...

Please throw the "quick start" in the trash can, where it belongs. And what are you hoping to prime the vacuum tubes with? The only "vacuum tubes" involved in this process are the vacuum line from the carb to the petcock and the four on the Carbtune. The ONLY thing that should be in those tubes would be AIR, with varying pressures, usually negative. There is nothing you can "prime" them with.

And before you ask, yes, carbs have been dipped twice this year with new o-rings.

Why twice? New o-rings each time? Unless you did not do the job properly and COMPLETELY, there is no need to do them again, and certainly not needing new o-rings, unless something got damaged.

It was running good at higher rpm till this point but struggled at low end and 2-3K.

Poor running at low throttle openings is a sign of clogged pilot passages.


You say the floats are "triple-checked". What setting did you use? Did you measure to the correct part of the float? Did you compare and balance BOTH sides of the float? Did you check the fuel level after the carbs were assembled?

And, ... while you might still have the numbers for your valve adjustment,
why not take advantage of the offer in my sig?

[gs11ezrydr]

Like said below Clean or replace the pilot jets and inspect and clean the adj. screws. try 1and1/2turns out up to 3 max and see what that does.

[Steve]

Like said below ...

Hard to read "below" when yours is the last post.

Oh, wait, you still have the (goofy) default setting for the forum that puts the newest post at the top.

That can be changed, so it reads more normally. And you can increase to 40 posts per page, too.

.

[cp___32]

The reason I have checked things multiple times was due to symptoms that I was troubleshooting in other posts at various points along my way to getting the bike running.

Like you suggested, Steve, problems at low throttle would indicate a problem with the pilot passages, so although I was thorough in my initial cleaning of the carbs, since you and others had suggested that might be the problem, I removed and re-cleaned the carbs to be sure it was indeed ruled out as an issue.

The same would be said about the float heights. Set float heights, bike runs wonky and may hint at fuel starvation, pull carbs, check floats, still running wonky, pull carbs to clean them, check floats again in case something was wrong.

The history on the bike was more of a general rundown of the last few months about what I had done so that people don't suggest "Have you tried cleaning the carbs? Have you tried setting the float heights? Yes and Yes, supposing those are good, what else would you check? Otherwise I'd be in an endless loop of cleaning the carbs.

I wasn't using the Carbtune to diagnose anything, simply an observation as I had the tubes connected in preparation for syncing once I got the bike running again.

I removed the carbs to do a bench sync because I've had trouble getting rid of the severe hesitation between 2-3K rpm and had removed the carbs check the slides on the diaphragms to see if there was a chance they might be sticking. (See my other threads on trying to troubleshoot the hesitation issue).

Since I had not been getting anywhere with cleaning and re-cleaning the carbs, ensuring the floats were set correctly, and all the other stuff, the final piece of advice I had not yet done was the valve adjusts. Hence why I did it.

[cp___32]

Must have overshot on my clearances. Getting between 75 and 90 psi compression (dry). They were around 120-130 psi before the valve adjust. I'll have to crack open the valve cover and shuffle some shims back. One one of the cylinders the 0.102mm shim fits, the 0.127mm does not for both intake and exhaust. I've got 75 psi compression. I read that since the clearances close as things wear it's best to stay on the larger size of things, especially with the exhaust. Should I bump the shim 0.05mm on both or just the intake side? I know my clearance is somewhere between about 0.105 and 0.125, and spec is 0.03 to 0.08. I guess ultimately the compression is going to tell me what range my specific engine wants to live in.

[cp___32]

Ok now I'm pretty confused. Went up 0.05 on both sides of Cylinder 1 and checked compression again. Still low. Just to see, I pulled the choke to see if that made a difference and sure enough I'm getting 150 psi. Adjusted the idle screw and I get 150 psi on cylinders 1 and 2. When the bike wouldn't start I was wondering if the idle screw was off so I tried turning it in and then back out with no luck.

Any thoughts on what to try next? BTW checked the float bowls and I do have fuel at the carbs. Just doesn't seem to want to pull fuel through. Clearly missing something here.

[Steve]

When you do your compression check, are you holding the throttle WIDE OPEN?
It's also supposed to be done on an engine that is at operating temperature, but you should still get decent readings when cold.

You are correct in that the max clearance specified is 0.08mm, but some of us will go as much as 0.10mm. I don't know of anyone that goes above that, certainly not as far as 0.125. The valve will be opened ever so slightly less ( roughly 0.05mm) but that should not be enough to affect compression readings.

.

[bobgroger]

Buy new pilot jets. http://www.ebay.com/itm/Mikuni-BS30-...pXmnIr&vxp=mtr
Check the starter jet. That is the passage between the bottom of the float bowl and the passage at the gasket area. You need to see light shined in the bottom of the bowl at the passage exit, and get spray of carb cleaner through the passage. It is too small to poke a wire through. It will NOT start if more than one of those is plugged, the choke will have no effect.

[londonboards]

You are using a mm feeler - aren't you?

I did a whole engine with an imperial (inch) one once.

Don't get caught up with compression testing. Your motor should fire in any case. Even low compression will get some combustion.

If it is not firing at all, and the plugs are not wet after a decent attempt to start, then you are not getting any fuel into those chambers. Check all plugs for dampness.

[cp___32]

People have posed the idea of new jets in my other posts. I gave them a thorough look over (as I do all parts) when I pull apart the carbs. I swapped out all the factory stuff for parts from a K&L carb kit with no difference in performance or lack thereof. The bike is completely stock except for electrical upgrades for reliability so why would a stock bike need new jets on all carbs?

Yes, I checked the plugs and noticed they aren't wet and the bike isn't flowing fuel. The only thing that changed between the bike running and not was the carbs came off and back on as a unit (without being taken apart) and the valve shims changed. I need to figure out why it's not pulling fuel through the carbs and into the cylinders.

[Brendan W]

Back to the petcock then starting with the vacuum line

[cp___32]

Both brand new, no leaks. And I am getting fuel to the float bowls. Drain them and they fill back up.