Amal Carb Pilot Circuit

I was reading the thread on carb cleaning and took a look at this link that is posted there:

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

It reminded me of something I found when going thru my carbs last spring that should be on everybody's list to check. I failed to post it previously but it is never too late I guess. Anyway rather than bury it in another thread I decided to start one.

When you look at the intake side of your Amal concentrics on the lower edge of the opening there are two holes drilled out, one on each side and one of them is plugged. This will make more sense if you take time to look at the above link, but one of them (the open one) is for air and the plugged one is for gas. Both lead to the pilot circuit mixing chamber. I was spraying some kind of cleaner into the pilot circuit to check that everything was open and discovered it was spraying out around the plug in the gas side of the circuit!

What this meant was that it was sucking air into the pilot circuit regardless of what I did with the adjust screw. I was having a hell of a time getting the bike to run right and during this process I cured a lot of things, but I am convinced that this was no small thing. It makes me wonder how many people are getting frustrated with the Amal carbs due to exactly this tiny little plug not sealing.

I goofed around looking for which goo I had on had that would seal it and finally wiped a small smear of high temp RTV over it. Put it on my list of things to keep an eye on and went riding. The RTV is orange so it is easy to see that it is still there doing the job.

Just a heads up.


Russ

Russ, thanks for posting that tip. It is something I will look for when I go to clear the pilot circuitry on mine. As an alternative, could you drill out or otherwise extract the plug and then press in a new plug turned up on a lathe? I thought silicone was not that resistant to gasoline?

Dave

thanks, that is a good tip.
There are two welsh plugs, the one you mention and the larger one that covers the pilot mixing chamber inside the bowl.
I suppose leaks at either would present fuel draw problems.
Good find.
I wonder if one could more permanently solder over a leaker vs use of sealant?
I'll give it a try on a spare toninght.

The pilot fuel gallery plug can always be replaced with a threaded plug.

Epoxy, like JB weld would work fine for that. OEM Quadrajet carbs were known from the factory for their casting plug leaks and a standard procedure for a Qjet - even a new one - included disassembling the carb and epoxying all the casting plugs. JB weld was one of the most often used epoxies by shops for this purpose.

I wasn't very thrilled with the silicone as a solution. It was what I had handy and I really wanted to get the bike out on the road. I didn't explain very well that this was one of the last items keeping me from riding after a full winter of going through the bike. I had some other products sitting around but all of them required more time to cure! The orange color makes it possible to pull back the boot and see that it is still there doing its job, but I think a more permanent solution should be found.

I had considered solder and wondered if my butane soldering iron would get it hot enough. I think LAB's idea of tapping it and threading in a plug is a good idea. I am not sure how one would test these plugs other than using a spray can or compressed air. Very miniscule leaks could be hard to detect. It was a near miracle that I noticed this leak. So it seems that the choice is to go full out and do some kind of "upgrade" or find something simple that can be reapplied but will not foul the carb. Maybe one of the Locktite products. Frankly I had pretty well forgot about it until I was looking at the pilot circuit cutaway in the attached article and thinking about what things to put on this winter's list of things to do.

MexicoMike said:

Epoxy, like JB weld would work fine for that. OEM Quadrajet carbs were known from the factory for their casting plug leaks and a standard procedure for a Qjet - even a new one - included disassembling the carb and epoxying all the casting plugs. JB weld was one of the most often used epoxies by shops for this purpose.

Click to expand...

L.A.B. said:

The pilot fuel gallery plug can always be replaced with a threaded plug.

Click to expand...

Both good tips, thanks.

Questions: If you had a threaded plug, could you use this route to clean out the pilot jet, instead of the more usual fix (drilling and tapping a hole in the carb body opposite the pilot air screw)? It would then be more accessible for a compressed air nozzle or a spray tube. Or could you direct the nozzle into the pilot air screw hole and flush it out through the pilot fuel gallery?

a threaded plug is a good idea at the airbox end as long as you don't get carried away, size wise and depth dependent. I would still seal it somehow. Rector #5 or Permatex non hardening brown gooey stuff.
The one inside the fuel chamber is bigger in diameter and there is precious little vertical room for threading, I don't feel comfortable threading on this one, maybe a little careful peening would suffice.
As far as cleaning I can't see anything better than the Jim Bush procedure. This allows direct access to the pressed in pilot jet restriction.
Reaching in from the airbox end would still require a 90* turn of whatever media is used. The open hole farthest from center already goes there anyway.
The basic construction is two parallel holes intersected at a right angle by the pilot mixture adjusting hole. The hole that is plugged allows a vacuum to be established resulting in fuel being drawn up from the bowl tube. The open hole is the air feed for mixing adjustment.
The slightly larger central hole terminates in the main fuel port that houses the main and pilot jet and needle and spray tube.
The fuel bowl is vented to atmosphere through the tickler as far as I can tell. Took me a while to see that.
I have a 932 body and slide on my desk if there are any other questions.

I think it's a 10-32 allen head set screw that I always use in the airbox side opening. I'd have to measure to be sure, but that size sounds familiar. It is a very easy process and can be done with a hand drill you will need the right taps. I've done 8 amals with this method and love having access to the pilot cicuit for cleaning.

AntrimMan and Britbike 220 — OK, I am now up to speed on this. Thanks.

I cannot solder zinc die castings.
I can do steels and coppers and brass with a flame and an iron like nobody's business.
It can be done as research indicates it is technically possible, I'm just not properly set-up.
Gasoila E-Seal looks promising and expensive.

I have just done this on my 2x MK1`s drilled out the plugs and tapped 2 BA i used 2 old pilot jet screws cut down fitted with the small "o" rings to seal them.
The rough idle has now gone it is as good as it came out of the factory.

I tried all sorts of carb/brake cleaner to get them cleared before i drilled them and non of it worked.

Thanks for the tip rvich.

I had a similar problem with slow engine speed running and starting after fitting a pair of new amal concentric carb bodies. Tried all the usual stuff and failed to solve the problem until I read your post today.

The 9mm diameter blanking plug on the under side of the carb body next to the main jet holder was leaking, is was possible to see tiny bubbles of carb cleaner around the plug when compressed air was blasted in through the mixture screw orifice.

The blanking plug appears to be aluminium, a careful tap in with a pin punch the same size has cured the leak.

Thanks again

Skoti

Most RTV sealers breakdown when in contact with gas (petrol).

While the openings around the plug are small, degraded RTV could get into the carb and muck things up. Granted, probably not too much, but a speck is enough to mess things up in the pilot circuit or the needle and seat.

I like the drill and tap method with a plug. Good tip.

Way back when the original post was current I took it upon myself to see if any easily obtained sealer would hold up against today's motor (American E10) fuel.
I went to a local Auto Parts, they had a comprehensive rack full of sealants and all only a couple of bucks each for a small tube.
I did buy around a half dozen different products all claiming to be resistant to gasoline exposure.
A smear of each was applied to a solvent washed coupon of aluminum roof flashing then allowed to air dry for 24 hours.
Each coupon was then immersed in gasoline contained within a clear glass jar, the jar then capped and left to sit for 24 hours on the desktop.
This was done individually following the same procedure, none of the sealants were ever in the jar together.
All sealants were dissolved by the gasoline during a 24 hour immersion.
It became obvious that a one part sealer that relied on evaporating VOC's at room temp would never work for this use and easily obtained one part sealers were all a failure.
I tried the JB weld since being a two part system it cross links and it remained hard after a week in the gasoline.
No particular epoxy product endorsement is intended, I just happened to have some on hand.
There were plenty of other two part epoxies on the manufacturing floor that would also work but I wanted to use something readily available to the average rider.
I also tested a product, which appears to be a pink coloured vinyl paste dissolved in MEK, as well as a red coloured cyanoacrylate thread locker on a screw and nut assembly. I won't use either of these with continuous exposure to gasoline.
Somewhere I have pictures and notes of each product test but suffice it to say only the cross linking epoxy was resistant to prolonged gasoline immersion.
I have also used this gasoline in a jar approach to test various hose products when I wanted to make up fuel line assemblies. Some of the clear product on the market becomes hard, brittle and unsuitable in very short order.
The moral: lacking prior experience, any product should be tested for compatibility with the intended use to determine suitability. Don't believe all the label claims. Understand the difference between resistant and proof. I do now.
The caution: an accident involving gasoline can be life changing. Any testing involving the use of gasoline is discouraged by me and conducted completely at your own risk.
All testing was performed in a controlled environment supervised by professionals. Do not try this at home. The state of the world we live in today requires the preceeding statement. Sucks but here we are.
Interestingly, the foam seal on the cap for the glass jar has resisted room temp gasoline vapors since the initial test roughly three years ago.
Looks and feels like a urethane product. Perhaps some promise there. I do have some urethane construction adhesive available so maybe another test is in the offing.
Keep in mind the purpose of the sealer is to permanently adhere and cure leaks, easy removal is not a requirement.
All the best.

Yep, As I posted 3 years ago, JB weld has been used for exactly this sort of issue at least since the 70's; works great. As noted, I'm sure other similar epoxy products would work as well but for whatever reason, JB Weld has become sort of a "standard" for such work. We used to joke to not trust anybody to rebuild Q-Jet carbs if they didn't have JB Weld in their toolbox!

Yep good ole JBW is holding together sealed a holed tranny in my car and a hole in fiber glass tank tunnel I caused in my buddy Wes's HiRyder tank. JBW cold weld as saved Trixie Combat cases punched out twice now by factory piston and later rod bolt let go. Can always just drill it out again if pilot clogs up with zine oxide crust. On the other hand good ole Rolls Royce Hylomar [Permatex owns now] would be a soft way to go with screw plug sealer.

In the old days of gasoline before catalytic converters almost all clogging was from trash in gas or it evaporating to leave shellac-varnish that simple organic solvents did the job, but now the lean burn = high oxygenation fuels make zn oxide pile up that organic solvents don't touch. Boil short a time in vinegar, soak in Pines-sol or Lyme Away and of course the expensive very toxic parts cleaners.