Am I the Pontius Pilate of this CX500?

Odontologist

Umina Beach, Australia....Where does that part go?
I've been having problems with my trial test rides around the block. Idles fine, but as soon as I give it throttle, it clogs down, as though it wasn't getting enough fuel. As soon as I let go the throttle to lower RPM, it's OK. Haven't been able to get past 4000 RPM. I knew, or at least, thought I knew I had rust in the tank, because when I moved it about I could hear a "slosh...slosh" with a definite feel of something scraping, like sand. It made sense, as the bike had been sitting in PO's shed for 19 years before I got it, and then another 2 in mine. Looking inside however, it looked pretty sound where I could see. The flow out of the petcock was slow and sometimes intermittent, so it had to be rust particles. I cleaned the petcock and tested it..flow was OK. I pulled apart the carbs....again...clean as a whistle.

Today I was determined to clean and fix the rust problem once and for all. I tried rinsing with distilled water several times and emptying...the sloshing continued. I gave up and hooked up a clear tube to a suction motor and separator I have, hoping to see what came out from the bottom of the tank......and this came out:



Now, some of the skeptics on here may looking in my direction, but I can assure you I DID NOT put that in the tank. After I got it I rode it once around the block. Never put fuel in. Removed the tanks and in storage until the recently for painting.

Have to put the carbs back together, fit them, and take for another run....see if that WAS the problem. Maybe yes....maybe not.

Cheers.
 

crazypj

Split personality, I fake being smart
Seems you have the dreaded 3 jet CV carbs problem. It is very common when stock air-box is removed. Unfortunately, I have no idea how to fix it as the carbs use different circuitry compared to the earlier CV carbs on CB350~CB500T and do not respond to the modifications I do on them. Fitting the original air box trumpets helps
 

Odontologist

Umina Beach, Australia....Where does that part go?
Thanks crazypj... can't do that. Need to stick to concept. I'll just have to fiddle with them until they work. Keep you posted.
 

Odontologist

Umina Beach, Australia....Where does that part go?
Trap for young (and not so young) players (Long post-sorry. Lot's to say and show)

I've been trying to get this bike running, but all I've managed is to run into problems.

I solved the usual "plastic bag in the tank" problem, so I was getting good flow out of the fuel tap. _/
I then had problems with the bike stumbling at around 4200 RPM, like running out of fuel or air. I made the assumption that my carbs were not as clean as I though, so I pulled them apart again and cleaned them...again. Turns out that the Penetrol I had painted them with sipped into a few crevices. What an IDIOT! Cleaned them throughly...again. In the process I broke a plastic non adjustable float that I was trying to adjust. Luckily I have a spare set of carbs for parts. Save.



Went out for a run and as soon as I opened the throttle the revs went up to around 4000 RPM and would not go down. When I rebuilt carbs the first time I followed Larry Cargill's carb book faithfully. I then had to pull them apart to clean the Penetrol paint that had sipped in and caused the slides to stick. When I put them together I DID NOT follow the book of Larry. I reassembled the bowls and top covers, so I couldn't sit them on the bench to align them properly, so I eyeballed it. They were not well aligned and one or both butterfly valves were sticking open.
I pulled them apart again and this time followed The Good Book....and problem solved.

Today I was able to do a few short runs around the block to dial pilot screws correctly, but it's bogging down as rpm goes up. Again gets up to 4200RPM and bogs down. I tried removing the tank cap in case the vent was blocked. Nope. Check the float levels. Good. WTF ?

I sat in my garage, just looking at the bike for a long time, thinking that after all I've done, I've failed to make the grade. As a novice builder, If I can't get a bike to run, then it's all over. I tried everything I could think off. I knew it was a carb problem but I just couldn't understand what.

Then, just as I was about to walk away, dejected, disheartened and beaten, a thought.....I wander.....Lets give it a go !

My original fuel tap has no filter, so to avoid contamination into carbs, I put an inline filter.





I wondered if the kink in the hose might be restricting fuel flow, especially as revs go up. So I replaced it with just a length of hose and no filter.



Took it for a run, and stumble gone. I'M BACK!

Closing anecdote: I was so happy that I just kept going around the block, until I ran out of fuel about 500m from home, and had to push the bike home. Who cares.

Anyway.........meet

[size=12pt]GOLDIE'S LITTLE SISTER[/size] (in homage of Cognito Moto's CB750 - One of my favourite builds and the inspiration to mine)


Image out of Pipeburn





















In the State I live in, if a vehicle is modified significantly like a whole different front end, then it may have to be assessed by an automotive engineer to enable road registration. I'm taking it to my mechanic for initial assessment and he will tell me if that is so. Until I get registration, I can't ride it. In fact my rides around the block were illegal. But she runs! Keep you posted.
 

der_nanno

Faster!
I keep on following this. If you use a petrol-filter, don't use the junk with just a mesh as you have the same kind of mesh already inside the fuel tank. Get a decent paper element filter, they are also available as very small ones – as installed on Mercedes-Diesels as pre-filters and they come from Mahle in Germany, so it IS decent quality.

You'd be amazed how much dirt comes from a freshly rebuilt tank and or from fuel-pumps at petrol stations.
 

Odontologist

Umina Beach, Australia....Where does that part go?
No doubt, and thanks der_nanno....but I'm having trouble finding one on a net search. Can you be more specific? Is it the whole filter or just the paper?
 

cxman

Active Member
DTT SUPPORTER
look for something in the 40-60 max micron range

often small genrators have good ones in that range

onan or kohler come to mind kohler has one that is 20 microns but may restrict wide open fuel flow without a pump

the standard cheapo filter can be in the 60-120 micron range or more and just pass the rust and crap particles right to the clean carbs i see it all the time

something like this will still flow enough fuel but catch crap get 2 carry a spare

https://www.amazon.com/KOHLER-25-050-22-S1-Diameter/dp/B0019MCOD4/ref=asc_df_B0019MCOD4/?tag=hyprod-20&linkCode=df0&hvadid=167120444362&hvpos=1o1&hvnetw=g&hvrand=16431235368214702578&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9009610&hvtargid=pla-314874625132&psc=1
 

crazypj

Split personality, I fake being smart
I actually prefer your build to the CB750 inspiration. Mainly, I've never been a fan of CB750 SOHC so something narrower and lighter is always a plus. As for fuel filters, the alloy body ones that unscrew to change filteruse either paper or nylon filters,find out whats available at local 'tuner store for Japanese imports. They were about $10.00 (US) last time I looked. If they are nylon filter element, you can swap it out for paper cartridge. Oh, the only thing I see wrong for inspection is direction indicators. You may have to fit Australian spec ones then swap back after you have plate on. I used to do MOT's in Britain, you could lose MOT licence for not doing them 'by the book' although things seem pretty slack last few years judging by some of ther bikes from UK posted on DTT
 

Odontologist

Umina Beach, Australia....Where does that part go?
Thanks fellas. And thanks for the tips re filters.
Crazypj, my brother told me exactly same thing re indicators and MOT. I'll take it to my mechanic who is also an inspector of unmodified vehicles so he can give me a list of possible defects.
 

irk miller

You've been mostly-dead all day.
DTT BOTM WINNER
They also make sintered metal inserts for those aluminum body filters. You may also consider a right angle filter, which is what I've had to go to on several of my bikes.

 

Odontologist

Umina Beach, Australia....Where does that part go?
I like the right angle set up. No kinks in line. The red filter can I showed has a sintered metal filter. I looked up what size particles these filter and its down to 30 microns. According to cxman this is the low limit before flow is restricted. Now I dont know if it was a kink in the line or the sintered metal filter. I think I'll get the Visu right angle with sintered metal and see what happens.
 

der_nanno

Faster!
These are the ones I always get (as can be seen in my thread-posts):

https://www.louis.de/artikel/kunststoff-benzinfilter-anschluss-6-0-mm-8-0-mm/10050018?filter_article_number=10050018&list=f369154f6a982b17acc69056eefe56c5

They sport both a 6mm and 8mm inlet and outlet. There's also dedicated 6 and 8mm versions available, but they aren't shorter by any means.
 

crazypj

Split personality, I fake being smart
What ever filters you get, check direction of flow. I've seen 'experienced' mechanics fit them backwards. Fuel flows around outside so you can see if they are working, I cut open a paper filter that looked brand new but was completely clogged inside. Spoke to the guy who fitted it and his reply was, who cares, sell them a new one. :mad:
 

Odontologist

Umina Beach, Australia....Where does that part go?
Well, just as I thought troubles were over, it started to hiccup again at 4000RPM. Could not get past this magic number.
It may be that all previous problems were contributing.....the poor flow out of the petcock caused by a plastic bag inside the tank, some shit inside the carbs which I failed to clean properly, the kink in the fuel hose from the fuel tap to the carb, my novice attempts at tuning carbs.......yes....all added to the problem.
But there was still one nail in my coffin.

I decided to run with some velocity stacks from a Ducati 9?? whose internal diameter match exactly to the carb intake internal diameter. Why? 'Cause they look so cool.



But to prevent birds and mice from setting up camp inside them, I concocted a filter made from some light foam and mesh, that seemed to me would not impede air flow.





In a last ditch attempt I removed these and went for another run....stumble finally gone, and here's a vid that proves it. 8) Any suggestions for a filter welcome. I thought maybe just the mesh. In any case, I decided to fork out for a set of Murray's carbs and they're on their way, but I wanted to make sure I learned something about carbs out of all this - specifically these old CV's. I did.

https://youtu.be/l9at0FZVXic
 

spotty

Vmax...why,yes i think i will
i'm assuming the thing that you learned was as rubbish as those carbs are, they don't weigh much when you're carrying the bin out to the street on garbage night

but well done for persisting
 

crazypj

Split personality, I fake being smart
Any kind of filter you put in a bell mouth will severely restrict air flow. The 'extra wear ' of unfiltered air would be minimal unless your riding on the beach or in a sandstorm. I found new rings around 10,000 mile intervals would put things back to normal, but, that was on a CB550 running at 8~12,000 rpm on a regular basis, with max of 9,000 should last substantially longer.
To run filters (I think you fitted the red ones backwards?) use a much longer fuel line looping around with filter at the bottom
 

Odontologist

Umina Beach, Australia....Where does that part go?
spotty said:
i'm assuming the thing that you learned was as rubbish as those carbs are, they don't weigh much when you're carrying the bin out to the street on garbage night

but well done for persisting
Jaja....These are the first carbs I ever clean and rebuild...AND get working again. I may not use them once the Mikunis arrive, but I'm never throwing them out. Or at least until the missus tells me otherwise.
 

Odontologist

Umina Beach, Australia....Where does that part go?
Not sure I want to do rings every 10-20K's Crazypj. Doesn't come that easy to me. I don't rides bikes that hard any more. But I would keep experimenting with different materials. Maybe some panty hose.
 

Odontologist

Umina Beach, Australia....Where does that part go?
I've put about 20km so far. Keep in mind that I have no road rego yet, so that's 20Km too many.

I'm waiting for Murray's carbs, and I need to adjust the rear shocks to stop the mini bounces, and in time, cut about 1" off both stands to make them useful, but I'm calling it....and I'm more than wrapped.

Thanks all for you kind words and hints along the way.
Mario

PS: What's next? I'm hooked.



















 
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