Sticky Mess in Head and Carb

Hey Guys,

A while back I post that my Mikuni carb was sticking due to a fiberglass tank wearing down on my '69 Commando. I have since replaced that tank, scrubbed the carb and manifold clean of all residue and have been riding for over 1,000 miles with no issue. Today while riding, the slide was stick so I pulled apart the Carb and found that the mess was back. A thick, sticky brown residue all over the slide, carb body, manifold and really, really, thick inside the head and valves.







I did a filter test on the gas and found no signs of fiberglass coming from the tank. The float bowl is also clean as the day i bought it. I was scratching my head and then noticed some brown flaky "dust" near the air jet. I then noticed a little of the same "dust" above the air filter on the joint between the frame tube and the support that the wiring harness runs through.



Hypothesis;

Glass bead residue from when i had the frame powder coater got in between the frame tube and support and is working it's way out and being sucked into the carb where it is mixing with the air / fuel mixture and causing the slide to "Gum Up" and is sticking to the intake in the head leaving a brown sticky residue.

Unlike my '74 there is no weld joining the frame and support.

I would love to hear your feedback. I feel like a my be "reaching a bit", but i want to feel confident and test all theories that may lead me to the cause. I am going to pull the head and have it cleaned and will rebuild it. Obviously i want to address the cause before remedying the symptom.



As always, All your help is appreciated.

Thanks,

I had exact same problem with my 70 fastback. Ditched the tank and bought an aluminum replica from Norvil. The tank had some fitting problems with the head steady but a nice difference. Nota cheap option but one that worked for me.
Mike

I've often wondered if fuel lines going hard from plasticizers leaching out of the lines and into the fuel would cause these kinds of problems or if it's too minute a quantity to worry about.

I am surprised your air filter did not do its job. ??????????????????

when the tank melted on my fastback it coated the slide on my mikuni and it coated the inside of the inlet manifold and gummed up my inlet valves holding them open and losing compression i now have a steel roadster tank ,,,,,,,,,,,baz

mikie3117 said:

I had exact same problem with my 70 fastback. Ditched the tank and bought an aluminum replica from Norvil. The tank had some fitting problems with the head steady but a nice difference. Nota cheap option but one that worked for me.
Mike

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Just to be clear. It's not he tank. The tank has been replaced and has been tested to insure clean gas is getting to the Carb.

The questions is;

What else could cause this? From your experiences, have you witnessed anything else cause this type of "gumming".

thanks,

Did you replace it with a metal tank though, or another glass tank ?

Mayby its the engine oil , from the breather ? if you have one? mist/fumes are piped into the air filter.

john robert bould said:

Mayby its the engine oil , from the breather ? if you have one? mist/fumes are piped into the air filter.

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I do have a breather with a catch filter. No signs of oil seeping from that and no oil in the air filer.

Rohan said:

Did you replace it with a metal tank though, or another glass tank ?

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It is a replacement Fiberglass tank. It's ethanol resistant glass and brand new. No signs of wear on the inside or showing when i ran gas through a filter to check for particles.

good luck on a so called ethanol resistant glass glass. you will NOT see signs of wear or particals in the fuel. it is a chemical reaction where it dissolves into the fuel.

jsouthard said:

It is a replacement Fiberglass tank. It's ethanol resistant glass and brand new. No signs of wear on the inside or showing when i ran gas through a filter to check for particles.

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bill said:

good luck on a so called ethanol resistant glass glass. you will NOT see signs of wear or particals in the fuel. it is a chemical reaction where it dissolves into the fuel.

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Is there a way to test the fuel that i have currently in the tank to see if there is in fact glass mixture in it?

How long does your bike set between re fueling? Ethanol will gum up any motor that it is left to set in.

Dennis

Check with vendor maker of the fiber tank as only Novalac resin is widely available at 'reasonable' cost for boats and aircraft booze solution. Spiked gasoline does not gum up anything by itself only some metals and organic chemical based components attacked and spread form there plus of course if enough moisture absorbed a water layer at bottom of containers. Carbonfibre as obnoxious as he was to be kicked off did leave good data on resins for me. Its also quite possible to have gotten a bad batch of gasoline with crap already in it such as comnoz noticed on a Texas top off that eventually destroyed his engine. A scientist might take some gas out the pump and some out of Norton fiber tank and cook off to see what remains.

I have a fair bit of experience with this on marine fiberglas fuel tanks. The symptoms you describe definitely fit the ethanol/fiberglass issues. As mentioned, you cannot SEE anything in the fuel because the resin is actually dissolved in the fuel. Most marine FG gasoline tanks have to be replaced with metal tanks. It's ironic because when these boats were made, only the very best quality boats used integrated FG tanks which essentially had an unlimited life in service, unlike metal tanks! Ethanol changed all that… Fortunately, diesel is not an issue so FG tanks on the diesel boats are still essentially bulletproof.

I purchased a new FG fastback tank from Burton's Bike Bits 4 years ago. Despite the fact that they explained it was made with ethanol-resistant resin, I coated it with Caswells before putting it into service. There has been no issues at all in the 4 years but whether that's due to the tank ACTUALLY being ethanol resistant or the Caswells preventing the problem, I can't say.

Caswell's two part tank sealer has worked a treat for Wes's tiny HyRyder tank and is Novalac resin.

+1 on ditching the fiberglass tank, or only putting ethanol-free gas in your tank. http://www.pure-gas.org


The ethanol is such a strong solvent that it will leach out even 50-year-old resin from a fiberglass tank. This resin will settle out once the ethanol evaporates, usually depositing what looks like tiny little black or brown droplets in the carbs, intake runners and valves.

I experienced this myself, and have seen it happen to other bikes with glass tanks - couple of Nortons and a BSA Victor.

I bought Caswell's sealer back in 2008 - it failed after two days. Mike Caswell said he'd send a new sealer he had just come out with, but it never came - neither did a refund.

I bought one of those Pakistani Roadster tanks, and spent two years fixing it until it stopped leaking (crappy welds). I'm told the new Indian ones are both better and cheaper

Hobot mentioned getting a chemist to cook of a bit of gas and see what's left. You could this yourself to some extent by putting equal amounts of gas from your Roadster tank and gas station in say a tunafish can and let them both evaporate out in the sun. I'd put little T-shirt material covers over the samples to keep crap out. When they're both dried up check for a residue. Tedious, yes, but the samples should evaporated down by the time your head re-done.

I bought one of those Pakistani Roadster tanks, and spent two years fixing it until it stopped leaking (crappy welds). I'm told the new Indian ones are both better and cheaper

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What ever become of the guy who was promoting, on this forum, the tanks he was selling? Said he tested them with 150 psi. He was offering to send a tank or two to a couple of members for a tryout. I never saw a followup.

What ever become of the guy who was promoting, on this forum, the tanks he was selling? Said he tested them with 150 psi. He was offering to send a tank or two to a couple of members for a tryout. I never saw a followup.[/quote]

150psi ? this guy must be *&^%@# joking, this amount of pressure will cause any tank to explode.

150psi ? this guy must be *&^%@# joking, this amount of pressure will cause any tank to explode.

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I took the 150 psi test as a clue to not send this guy any money.