Topic: Help to analyse compression test results

[Mikal]

Thanks all. I don't have tryed motorbike yet.  My mechanic told me something about " ...is not pushing/going up at high revs"
I will ask him better about this (if I correct understood...).
Today I tried only to run the throttle while motorbike engine was on (I don't have insurance yet to run on the road).
Engine is fast to go up revs but if I open too fast the throttle, it shutdowns, is this normal?

Well, mine has done 80 000km, and is a 500. Had it for three years now and I have never ever been able to snap the throttle open, too much air and it bogs down. It's just the nature of the beast I guess.

When everything is clean, synchronised, adjusted etc etc she will sing Like this:

And not like this (from when I bought it):

[calj737]

Mark -  A few comments:
I am not convinced your Mechanic properly cleaned your carbs for 2 reasons: If fully and properly cleaned, the bike would not require a "starting fluid". And, if the carbs are not fully cleaned, it is also possible that the slides are not synchronized and thus, your compression readings will also be negatively effected.

All your reports from riding indicate a poor state of tune and dirty carbs. Get these things done personally or professionally with a guarantee of their results.

There is no benefit to using higher octane fuel in these bikes. The stock compression ratio is about 9.2-9.5:1. This is very well suited to 89 octane. Higher octane fuel only produces benefit with higher compression engines. A fuel additive like "SeaFoam" while beneficial for daily/seasonal treatment of your fuel for Ethanol-based fuels will do virtually nothing for carbs that are not cleaned properly. SeaFoam will not dissolve varnish from fuel evaporation due to prolonged storage.

[bochnak]

So if I'm reading the graph correctly, you have 103-110psi across all 4, correct?

D'oh, I see how to read the graph now. That is a neat tool, however I don't see why anyone needs to spend the extra dough on a graphing feature. A pencil and notepad are pretty these days.

To the OP, along with what everyone else mentioned, make sure you check for vacuum leaks.

[strynboen]

these" registrators" is common in Europa..they fit in the car logbook..and is fine for dokimentasion ..in sale or reparation..its nice to hold the messurings..and by tvisting the plate you can make a later test and hold them up..against the erlyer test

[_mark]

Hi guys I will keep motorbike tomorrow.

Today I've spoken with the mechanic about the problem of cold starts; he told me that the reason are not the carburators.

If it is for real due to carburators, what is the difference between a cold and an hot start from carburators point of view?
 
The reason of fail to start in cold conditions is because of the lack of compression; once the engine is started and warm the problem disappears because some of the compression is recovered.

Any comment? Thanks a lot.

[calj737]

A cold engine not running is creating less vacuum than a running engine. Less vacuum creates less fuel draw, and reduces the atomization of the fuel. Choke enriches the fuel mixture making it easier to combust. You should never have to use a Starting Fluid. If so, you are not getting proper amounts of fuel into the combustion chamber. This has virtually nothing to do with a lack of compression.

Another indication of poor starting can be related to ignition and spark. Poorly timed ignitions, poorly gapped points, weak condensers all contribute to poor spark and poor combustion. Once warmed up, these components can improve their effective performance because they are not working so hard on cold fuel and inside a cold engine.

If your bike won't start with choke after a crank or two, you have a tuning issue. Carbs or ignition. Simple as that.

[strynboen]

a veared aut engine starts fine..its use a lot of oil..or rattel..but starts fine...so find an other mecanic ..-he dont have any idea of this type engines....old diesel engines...dont start easy..bu kompresion lost..but a small gas engine..dont have this problems...

[_mark]

Hi. Today I rode my bike. I post here some videos I did while it was stopped after 3 hours (almost cold conditions):

when is cold the minimum is lost but we are talking of a inimum of 800 rpms . Rpms are increasing smooth and fast. For the moment I keep the bike as it is and then i will see how behaves in the next tousands Kms.

Thanks. Regards

[calj737]

It would be entirely helpful to us, if you would explain the "Starting procedure" you used in the 3 different videos. Did you use CHOKE for video 1 or video 2? Why did the RPMs increase in video 3?

The camera pointing at the handlebars and the seat is about as useful as a hammer in flood.

Do you know the proper technique for starting your bike? You should use CHOKE for the first couple of minutes until the motor warms up, then remove the CHOKE, then determine where the idle RPM is.

[_mark]

video 1 and 2 were recorded some moments later (let's say 1 minute) after I start the bike with chocke comand ON .After this minute I released the choke command and I start to record the videos. So in no one of the videos I used the choke.
In video 3 the RPMS were slighty over 1000 because the throttle was twisted a little.

The pourpose of my video was to undestand if the minimum is good in cold conditions and without choke (video 1 and 2)and to know also if the response of the throttle is good (video 3)

Thanks

[Stev-o]

The pourpose of my video was to undestand if the minimum is good in cold conditions and without choke

Thanks

If you are referring to the RPM setting, it needs to be set once the engine if fully warmed up [5-10 min].
I set it by ear, the gauges on these bikes are not super accurate, can be off 10-15%.
And I like the idle a little higher than what the manual states, about 1500 rpm.

[_mark]

thanks. Could be helpful a smartphone app to understand RPMS ? is possible?

[grcamna2]

I know it has been mentioned but did your mechanic do the full 3000km service including adjusting the valves,cam chain,points,timing,replacing the plugs and synchronizing all 4 carburetors? I am also curious if the carburetors may have dirt in the small pilot jets(possibly coming from the fuel tank?)which would cause an erratic idle speed.

[_mark]

Yes, everything : cam chain checked, valves clearance , timing , new condesnators, new sparks, complety revised carbs ( I think kit from kyster), new manifolds, new points,  new battery, new pinion sprocket and chain etc

new tyres and frame incision and adjustion also ( see here what happened...   http://forums.sohc4.net/index.php/topic,152832.msg1764733.html#msg1764733   )

Thanks

[Stev-o]

complety revised carbs ( I think kit from kyster),

This could be problem. Keyster = Krap

Only use Keihin parts!!

[DaveBarbier]

Yes, everything : cam chain checked, valves clearance , timing , new condesnators, new sparks, complety revised carbs ( I think kit from kyster), new manifolds, new points,  new battery, new pinion sprocket and chain etc

new tyres and frame incision and adjustion also ( see here what happened...   http://forums.sohc4.net/index.php/topic,152832.msg1764733.html#msg1764733   )

Thanks

Diachii condensers? They often cause problems also.

[grcamna2]

complety revised carbs ( I think kit from kyster),

This could be problem. Keyster = Krap

Only use Keihin parts!!

+1 

[_mark]

complety revised carbs ( I think kit from kyster),

This could be problem. Keyster = Krap

Only use Keihin parts!!

 

[calj737]

complety revised carbs ( I think kit from kyster),

This could be problem. Keyster = Krap
Only use Keihin parts!!

Bingo! I hope your Mechanic didn't replace your stock jets and needles with Keyster products. If he did, go back, kick him in the teeth, and demand your stock parts back. The original brass parts for your carbs will last a lifetime unless they are mangled by someone.

There should also not have been a reason to change from stock sizes based upon a stock motor, and proper tune. Hopefully, he only used the gaskets and o-rings and didn't touch your brass.

In videos 1,2 your engine idle is so low that its impossible to tell if the carburetors are vacuum synched. With the RPMs holding around 1,200 you should have a very smooth idle and little to no vibration from the motor. If you hear "clunking" or "stuttering" than your carbs/ignition need further attention.

[_mark]

I don't know if I had the stock jets from beginning. Replacement was needed because when I bought the bike the throttle command was stuck in two carburators.

At 1200 rpms the engine is smooth and regoular with no esitations even in cold conditions.

Thanks

[calj737]

I don't know if I had the stock jets from beginning. Replacement was needed because when I bought the bike the throttle command was stuck in two carburators.

Fair enough, but stuck SLIDEs has nothing to do with your JETS and NEEDLES.

[_mark]

I don't know if I had the stock jets from beginning. Replacement was needed because when I bought the bike the throttle command was stuck in two carburators.

Fair enough, but stuck SLIDEs has nothing to do with your JETS and NEEDLES.

the slide is not connected directly to the needle? thanks regards

[calj737]

It is, but "Stuck" slides don't require replacing needles. Damaged needles to erosion/corrosion/bending necessitates it.

I'm not trying to harp on you/your mechanic, simply providing you insight into how truly critical certain components (especially in your carbs) are. Your mechanic may have a casual opinion to replacing the stock brass in carburetors, but it is extremely well proved here that stock/aftermarket brass are very different, especially the needles. When someone gets a 40 year old machine with gunked up bits, they think, "I'll replace this, replace that with all new shiny bits". When in fact, you're hurting yourself because those grungy old bits once cleaned, are actually better than the shiny new ones (unless made by the same manufacturer Keihin). So just giving you a heads up.

Enough said, carry on and keep posting your progress 

[bochnak]

I have used Keyster kits several times with no issues. They are the only kit that comes with the emulsion tube, which can wear over time.

Not to hijack, but what were some of the negative experiences with Keyster kits?

Thanks,
Matt

[grcamna2]

I have used Keyster kits several times with no issues. They are the only kit that comes with the emulsion tube, which can wear over time.

Not to hijack, but what were some of the negative experiences with Keyster kits?

Thanks,
Matt

the new Keyster brass stuff seems mismatched and generic which causes poor/too rich,etc. carb. performance