RunRyder RC
WATCH
 2 pages [ <<    <    ( 1 )     2     NEXT    >> ] 2904 views POST REPLY
HomeAircraftHelicopterGasser Model RC HelicoptersOther › carburetor primer bulb
10-17-2005 05:50 AM  12 years agoPost 1
Pre-Mix

rrApprentice

U.S.A.

My Posts: All  Forum  Topic

Ran the Predator for the first time this weekend and am very pleased with the results. The engine was very smooth for the first few tanks. What I noticed on day two was that the idle was no longer smooth and the primer bulb was almost empty at idle. Further investigation revealed that the insulator block was leaking a bit, so will have to fix that. My question is: when the engine is idling, should there be fuel flowing back to the tank via the return line? For that matter, should fuel be flowing back to the tank via the return line at any RPM?

Johan

PM  EMAIL  GALLERY  Attn:RR  Quote
10-17-2005 07:01 AM  12 years agoPost 2
FCM

rrElite Veteran

Surrey, England

My Posts: All  Forum  Topic

Yes and yes I think Johan.

I always have some air in my primer bulb but have had problems with it emptying on one of my Walbro's which turned out to be a faulty check valve in the carbi body.

Paul.

PM  EMAIL  GALLERY  Attn:RR  Quote
10-17-2005 07:18 AM  12 years agoPost 3
Pre-Mix

rrApprentice

U.S.A.

My Posts: All  Forum  Topic

interesting
Hi Paul,
So, when I fix the leaky intake manifold and find that there is no fuel flow to the tank via the return line at idle, then there is another problem. The reason I ask is this is a good way to tell if the carb is pumping at 100%. It sounds like mine may be borderline. If someone can please go and idle their heli and confirm if there is indeed fuel bypassing the carb and going back to the tank, I would really appreciate it.

Johan

PM  EMAIL  GALLERY  Attn:RR  Quote
10-17-2005 07:56 AM  12 years agoPost 4
FCM

rrElite Veteran

Surrey, England

My Posts: All  Forum  Topic

I will be idle running my Benzine this afternoon (603 carbi) and I will see if it does return fuel at idle.

Paul.

PM  EMAIL  GALLERY  Attn:RR  Quote
10-17-2005 08:01 AM  12 years agoPost 5
TEKHD

rrApprentice

Fresno,Ca USA

My Posts: All  Forum  Topic

Pre-Mix
Yes It doses send the unused fuel back to the tank. The higher the RPM less fuel is sent back.In a normal carb there is a ACC pump to supply fuel on demand. On walbro carbs the fuel flow is constance the engine just takes what it needs from the fuel stream.

The Best Place To Be Is In The Air

PM  EMAIL  GALLERY  Attn:RR  Quote
10-17-2005 09:43 AM  12 years agoPost 6
Pre-Mix

rrApprentice

U.S.A.

My Posts: All  Forum  Topic

Paul, please do let me know what you find when you idle your machine.
TEKHD, what you say makes sense that the fuel return rate should be highest at idle. This system is very similar to fuel injection where the fuel just circulates past the injectors and they only use what they need.
Im starting to think that I have more problems than just a leaky insulator block. Will have to do some carb surgery tonight.


Johan

PM  EMAIL  GALLERY  Attn:RR  Quote
10-17-2005 10:40 AM  12 years agoPost 7
FCM

rrElite Veteran

Surrey, England

My Posts: All  Forum  Topic

Just finished running it and it doesn't work how I thought it would!

After starting and letting it warm up a bit, I disconnected the return line and guess what - nothing came out! I tried opening the return line at two places, at the carbi connection itself which faces down and where I refuel just close to the tank and both gave me nothing!

I did check that the fuel bulb was full and it looked as per normal - full with a small air bubble in it. After stopping and draining the fuel, I manually pumped the carbi and lines dry as per normal so the bulb/pump is definitely working as it should.

I have no explanation for this. I too was expecting a fair flow of return fuel as the engine is barely using any at idle. Maybe the pump doesn't pump much at idle RPM?

Paul.

PM  EMAIL  GALLERY  Attn:RR  Quote
10-17-2005 05:07 PM  12 years agoPost 8
UK Helinut

rrApprentice

Gloucestershire

My Posts: All  Forum  Topic

Fuel dose not return to the tank during an engine run.

The line is an overflow for the priming system. Quite a ew people don't run the line back to the tank.

PM  EMAIL  GALLERY  Attn:RR  Quote
10-17-2005 05:13 PM  12 years agoPost 9
UK Helinut

rrApprentice

Gloucestershire

My Posts: All  Forum  Topic

Forgot to mention, the problem you have with the primer bulb bieng empty.

It could be running the engine a little on the lean side. Check your plug colour. If this is OK, you may find that the fuel metering neadle is not lifting enough by the diaphram.
If you are still having problems PM me and i will try to help you out.

PM  EMAIL  GALLERY  Attn:RR  Quote
10-17-2005 08:41 PM  12 years agoPost 10
UpstateRotor

rrApprentice

Upstate NY

My Posts: All  Forum  Topic

Seems as though a few of us have some misconceptions as to how a Walbro carb works.

Please read:

http://www.wind-drifter.com/technic...rviceManual.pdf

PM  EMAIL  GALLERY  Attn:RR  Quote
10-17-2005 09:33 PM  12 years agoPost 11
jackheli

rrProfessor

Vancouver - Canada

My Posts: All  Forum  Topic

UpstateRotor:

Excellent link. Thank you for sharing.

It's easy to find an excuse to do wrong. Hard is not to find an excuse to do right.

PM  EMAIL  GALLERY  Attn:RR  Quote
10-18-2005 04:01 AM  12 years agoPost 12
FCM

rrElite Veteran

Surrey, England

My Posts: All  Forum  Topic

That's a great download - thank you UpstateRotor.

After reading it, I now realise what a clever chappy Mr. Walbro is

Paul.

PM  EMAIL  GALLERY  Attn:RR  Quote
10-18-2005 04:13 AM  12 years agoPost 13
Pre-Mix

rrApprentice

U.S.A.

My Posts: All  Forum  Topic

Thanks!
Thanks to all who have contributed to this link. The download definitely takes away the mystery of the return line.
Just for the record. My engine was running/idling fine with a dark tan plug color for the first 6-7 tanks. It was only after I noticed the idle to surge a little bit that I inspected further to find a small amount of fuel on the bottom of the insulator block. Also I noticed that the primer bulb fuel level was very low.
I then removed the carb and insulator and found all to look OK. I reinstalled everything and the heli once again ran quite nice with a steady idle until I flew around for about 3/4 tank. The idle once again started surging and also found the plug to be a lighter tan which would indicate not a lean run but the engine definitely leaning out a bit. At that stage I called it a day and posted here on RR.
The insulator block is perfectly flat as I decked it on both sides before I started the engine for the first time. Post run inspection revealed that its still flat. Possibly the mounting surface on the cylinder itself may be suspect so will deck that with a sharpening stone.
As for the carburetor, will inspect/clean the fuel inlet screen and try again. If anyone has alternate suggestions please let me know.

Johan

PM  EMAIL  GALLERY  Attn:RR  Quote
10-18-2005 06:00 AM  12 years agoPost 14
FCM

rrElite Veteran

Surrey, England

My Posts: All  Forum  Topic

Johan, it sounds like your insulator block is leaking after the engine has got hot. I am experimenting with different ways to seal the block against the engine at the moment.

What I have tried already is to use some high temp. red RTV that I saw somebody was using here together with a Zenoah gasket and using only a light torque on the mounting screws together with thread lock.

The results were, after flying it for 75 minutes, that the block did not leak at all hot or cold but the RTV, unsurprisingly, had swollen up so that when you looked down the intake, you could see a complete thin line of red RTV as it had expanded and forced its way out of the joint.

I have removed it now and instead am using some spray high temp copper gasket adhesive together with a gasket and will be flying this tomorrow. This stuff is supposed to be petrol resistant - we shall see!

The RTV may never actually leak in service and due to its rubbery nature, fills the gap caused by heat distortion really well. I may go back to using this another time when I can spend more time testing to see what the long term effects are.

Will let you know how the flying goes tomorrow.

Paul.

PM  EMAIL  GALLERY  Attn:RR  Quote
10-18-2005 06:57 AM  12 years agoPost 15
Pre-Mix

rrApprentice

U.S.A.

My Posts: All  Forum  Topic

another option
Hi Paul,
Sparky666 is also doing the RTV route and has had good success in doing so. Im sure if it is used sparingly it should do the trick. Im going to try an aluminum intake block which is mounted with a teflon plate as an insulator. Im going to try one up this afternoon and see how well it works. No gaskets are required on the teflon, only between the carbie and the AL block. I can send some pics if you like. Keep us posted on your findings!

Regards, Johan

PM  EMAIL  GALLERY  Attn:RR  Quote
10-18-2005 09:11 AM  12 years agoPost 16
FCM

rrElite Veteran

Surrey, England

My Posts: All  Forum  Topic

Oh yes, please do post/send some pics of this aluminium block - sounds very interesting to me. I wonder if the carbi spacing from the engine cylinder will be the same though? Difficult for me to use this if it isn't the same as the standard Zenoah item.

Paul.

PM  EMAIL  GALLERY  Attn:RR  Quote
10-18-2005 09:33 AM  12 years agoPost 17
Pre-Mix

rrApprentice

U.S.A.

My Posts: All  Forum  Topic

Paul, I will measure it up and post the data here as soon as I get it.

Johan

PM  EMAIL  GALLERY  Attn:RR  Quote
10-18-2005 07:01 PM  12 years agoPost 18
UK Helinut

rrApprentice

Gloucestershire

My Posts: All  Forum  Topic

Also check that the bolts holding the carb to the insulator block are not too long , they could bottom out on the engine block and jack the insulator away from the engine. This is a very common fault with the zenoah, that leads to a blown gasket.

PM  EMAIL  GALLERY  Attn:RR  Quote
10-19-2005 05:41 AM  12 years agoPost 19
Pre-Mix

rrApprentice

U.S.A.

My Posts: All  Forum  Topic

will do
UK heli nut, will check those bolt lenghts.
I decked the intake surface on the cylinder and found it to be quite uneven. So no matter how flat my insulator block was, i think this was the root cause for the leaks. So if anyone else is struggling with intake leaks, be sure to check the cylinder itself for flatness.

Johan

PM  EMAIL  GALLERY  Attn:RR  Quote
10-19-2005 01:23 PM  12 years agoPost 20
FCM

rrElite Veteran

Surrey, England

My Posts: All  Forum  Topic

Flew with the copper gasket adhesive on the insulator block. Okay at first but after about 30 mins, noticed it was leaking a bit. Flew a total of 40 mins. When I got home, stripped the carbi off and it was easy to see where it had been leaking. It looks as though it may not be the fault of the copper adhesive but may be due to the lead composit gasket I used with it. The adhesive seems to have washed off of the gasket.

I also checked my carbi bolts but they are well short of causing any problem - good tip though!

I have used the same gasket adhesive on my cylinder base gasket and this is holding up well so far with no leaks. The gasket I used was a home-made cardboard effort but I think due to the porous nature of the cardboard, the adhesive has taken to it better so I will be trying a home-made insulator block gasket next. Not sure whether to use the gasket adhesive or RTV though - will sleep on it and decide tomorrow

Paul.

PM  EMAIL  GALLERY  Attn:RR  Quote
WATCH
 2 pages [ <<    <    ( 1 )     2     NEXT    >> ] 2904 views POST REPLY
HomeAircraftHelicopterGasser Model RC HelicoptersOther › carburetor primer bulb
 Print TOPIC  Make Suggestion 

 3  Topic Subscribe

Wednesday, September 19 - 12:23 pm - Copyright © 2000-2018 RunRyder   EMAILEnable Cookies

The RC discussion world needs to consolidate. RR is now one choice for that. Its software is cutting edge. It hosts on-topic advertising. Help RR increase traffic buy making suggestions, posting in RR's new areas (sites) and by spreading the word.

The RunRyder Difference

• Category system to allow Rep/Vendor postings.
• Classifieds with sold (hidden) category.
• Classifieds with separate view new.
• Answer PMs offsite via email reply.
• Member gallery photos with advanced scripting.
• Gallery photo viewer integrated into postings.
• Highly refined search with advanced back end.
• Hosts its own high end fast response servers.
• Hosts thousands of HD event coverage videos.
• Rewrote entire code base with latest technology.
• No off-topic (annoying) click bait advertising.
Login Here
 New Subscriptions 
 Buddies Online