Sticky Slides

[geodoc]

Sounds like result from one of those "what's your stripper name" generators .......................... ah, hum ................. Though my favorite is "Icy Streets".

Actually, I wonder if anybody else with dellorto 40mm PHM carbs has encountered a slide sticking problem. The bike is a Tonti hybrid with LM1 spec heads, 620X10 cam and various other adulterations. The 40mm carbs were bought new and after about 1000 mi., the LH carb started to stick just above idle. I had it apart a half a dozen times looking for problems, but there were none. Likewise, no throttle, cable or splitter problems either. The sticking would only occur only when running. With the engine off, slide return was consistent with a nice 'snap'. In frustration, I replaced the carb after I sent it in for inspection to Herdan, just to be sure that there was not some subtle defugalty that I'd missed (he couldn't find anything).

With the replacement carb, all seemed well until about the 2500 mi from new mark, the RH carb starts with the same thing. I had the lightest carb springs in from the start and though installation of the heaviest would overcome this tendency for a while, even the heavy springs wouldn't prevent it after a while.

In frustration, I've been googling around and come upon an interesting suggestion from some bike forum discussing a like problem on an XR650 or somesuch. The conclusion there was that ethanol fuel reduces the "lubricity" of the fuel to an extent that with slide - bore fit in anything less than new condition, that lack of lubricity allows the slide to stick when it's most susceptible - near idle when it presents a large surface area to engine vacuum.

The suggested fix was to add a dash of lubricant to ethanol fuel to prevent this problem. I have not yet had a chance to try this out, weather having turned to usual Vancouver BC drizzling, bleak, sodden gloom. Thinking that a small squirt of Marvel Mystery (etc.) might counter the lack of lubricity and hopefully make all right in the world, even allowing light carb springs again and thus the need to shop for a bionic RH forearm implant too.

 

[john zibell]

The fuel isn't the problem. The slide or carb body is. My guess is a slight restriction low in the carb body. Perhaps a light touch with crocus cloth near the bottom of the barrel of the carb may cure it. If not try stiffer carb return springs. The 40s on my MkV work flawlessly even with soft springs. BTW, I'd say 40 mm carbs with MkI heads is a bit too big. 36s would probably be more efficient.

 

[geodoc]

Like I mentioned above, I ended up with the heaviest springs of the 3 rates available. That was sufficient for a while, but eventually it wasn't. The slides and carbs started out new and showed no sign of burs, rough or warn places or deposits. I spent a fair amount of time polishing the surfaces of the slides and the bores too, but to no avail. This is what has me interested in the ethanol / lack of lubricity angle. I'm picking up a bottle of Marvel Mystery oil in the next few days and when the weather is conducive, will test it out, see if the problem remains and report back.

I talked the carb size over with Mike Rich who did the head work converting (appropriately) Convert heads to LM1 spec) a fair bit before going for the 40mm's. It may be that at lower throttle positions that it would be somewhat better mannered w/ 36's (though it's quite acceptable w/ 40's, even more so with the 2-into-1 exh. with a cross-over added and hope for better still w/ anti-reversion cones that I made but have yet to install). This bike BTW is not an 850cc displacement, but a 917cc (86.5mm bores - 850T barrels bored & nikasiled w/ JE pistons to suit).

The fuel isn't the problem. The slide or carb body is. My guess is a slight restriction low in the carb body. Perhaps a light touch with crocus cloth near the bottom of the barrel of the carb may cure it. If not try stiffer carb return springs. The 40s on my MkV work flawlessly even with soft springs. BTW, I'd say 40 mm carbs with MkI heads is a bit too big. 36s would probably be more efficient.

 

[DanPez]

The bike is a Tonti hybrid with LM1 spec heads, 620X10 cam and various other adulterations. The 40mm carbs were bought new and after about 1000 mi., the LH carb started to stick just above idle. I had it apart a half a dozen times looking for problems, but there were none. Likewise, no throttle, cable or splitter problems either. The sticking would only occur only when running. With the engine off, slide return was consistent with a nice 'snap'. In frustration, I replaced the carb after I sent it in for inspection to Herdan, just to be sure that there was not some subtle defugalty that I'd missed (he couldn't find anything).

With the replacement carb, all seemed well until about the 2500 mi from new mark, the RH carb starts with the same thing. I had the lightest carb springs in from the start and though installation of the heaviest would overcome this tendency for a while, even the heavy springs wouldn't prevent it after a while.

near idle when it presents a large surface area to engine vacuum.

You hit it on the button when stating that the slides, near idle presents a large area.
The intake port is almost completely closed and having the piston volume creating vacuum the slide will have a tendency to be pulled in.
With the performance cam you have an additional vacuum intake causing the slides to be pulled in even more.

Have you tried lubricating the slide guides ...ever so slightly?

 

[geodoc]

Heh Dan,

No, can't think of any lubricant that could be applied to the slides or guide pins that would not either gum up or dissolve in fuel. The dash of oil in the ethanol-laced fuel idea is all I can think of.

Interesting though that the 1000LM and Sport 1100 w/ 40mm's and milder cams don't necessarily seem to have this issue. At least nobody here's brought up ones that did.

You hit it on the button when stating that the slides, near idle presents a large area.
The intake port is almost completely closed and having the piston volume creating vacuum the slide will have a tendency to be pulled in.
With the performance cam you have an additional vacuum intake causing the slides to be pulled in even more.

Have you tried lubricating the slide guides ...ever so slightly?

 

[Series4]

First response would be to try it with non-ethanol fuel if you can find it. Second would be to try a metallic anti-galling compound like Coppaslip or the Loctite nickel-based equivalent. The carrier oil will be washed off but the metallic base should remain.

Of course neither is a sustainable solution (pun intended) but perhaps the best option is a synthetic 2 stroke oil. Mobil Racing 2T is the only one I've had experience with, if it can protect a 2 stroke engine it should lubricate a throttle slide and it will b available from service stations and hardware stores

 

[Chris R]

That is an interesting one - I run the lightest springs possible on both my lemans 1 and V and no problems.

Gunkote/Dow Corning Molycote?

 

[geodoc]

I wonder if it has something to do with the 620X10 cam and the porting as compared to your LM 1 & 5? Do you have the stock B10 cam in the LM5 and the stock "lawnmower" cam in the LM1?

That is an interesting one - I run the lightest springs possible on both my lemans 1 and V and no problems.

Gunkote/Dow Corning Molycote?

 

[Chris R]

The lemon is an X10 and the Mark V is stock so hmmm. You'd think at low rpm/small throttle openings there would be less vacuum with a more radical cam, no? Unless it opening happens as you rapidly close the throttle. I can't see the amount of alcohol in the fuels these days causing this but you never know. Just a random 2 o'clock in the morning thought - any possibility it is carb icing? And yes alcohol makes that worse.

By the way, as far as I can see Marvel Mystery oil is a bit of a belts and braces crock. Yes the aero boys swear by it but they also insist on super leaded gas in engines that have only a 7-1 compression ratio. As far as I can see it is basically two stroke oil. Yes run two stroke oil to preserve your exhaust but don't expect it to help 'top end oiling' or such other non-problem problems.

 

[geodoc]

It seems to be sticking just on the over-run throttling down towards the idle stops. I've drained the tank & carbs yesterday and put in some Chevron 94 that's available here in Canada and is labeled "contains no alcohol" on the pump. Amazing we can still get that up here. All the rest of the grades do have it.

I've been purchasing premium in the US for the Eurovan and in jugs for the bikes. The local price for Chevron 94 is $1.56 /lt. or ~$5.90 CDN /gal. and close to that in USD. Across in the US / Wash. it's about $4.00 / gal. As soon as there's a sufficient lull in the rain, I'll take it out for a moderate duration burn and see if I get sticking just with different fuel, but nothing else.

Yeah, the recip aircraft world swears by MMO. I've seen it actually work to remedy sticking valves in a Beaver with a R985 radial. Have also seen a case where there was a Cessna in storage for a long time that stuck some rings and was pumping oil like crazy even after a few hours of hard running. MMO in the oil got them unstuck and saved a top end removal, for a while anyway until it had to come off for other reasons. It appears that MMO is more solvent than lubricant. Though that might be a good thing since I'm reading that ethanol tends towards leaving more in the way of intake tract deposits as well.

The lemon is an X10 and the Mark V is stock so hmmm. You'd think at low rpm/small throttle openings there would be less vacuum with a more radical cam, no? Unless it opening happens as you rapidly close the throttle. I can't see the amount of alcohol in the fuels these days causing this but you never know. Just a random 2 o'clock in the morning thought - any possibility it is carb icing? And yes alcohol makes that worse.

By the way, as far as I can see Marvel Mystery oil is a bit of a belts and braces crock. Yes the aero boys swear by it but they also insist on super leaded gas in engines that have only a 7-1 compression ratio. As far as I can see it is basically two stroke oil. Yes run two stroke oil to preserve your exhaust but don't expect it to help 'top end oiling' or such other non-problem problems.

 

[geodoc]

Had a chance to ride the bike now with the ethanol fuel drained and Chevron 94 no-ethanol fuel in the tank. Presto ................ no sticking.

Turns out that there is a little more to the story. Talked to Mike RIch this morning to order some valves and recounted the saga. He told me that mine is only one version of this problem. The actual issue is not so much the ethanol itself in the fuel, but the fact that some plastics and resins used in fiberglass tanks (like mine) are soluble by ethanol. So that is actually my problem. The ethanol premium fuel that I was getting in the US was dissolving the resin in my fiberglass tank and causing the slides to stick. So with a steel or aluminum tank it's not an issue.

 

[john zibell]

geodoc,

Thanks for the good reason. Have you ordered your metal tank yet?

 

[geodoc]

nope ................ as long as I can still get Chevron 94 octane w/o ethanol, I'll just keep using that & not dissolving my tank. If 94 stops being available then it's tank liner I guess. I will let Manel, the maker of the tank know though. Surely there must be a resin available that resists ethanol.

geodoc,

Thanks for the good reason. Have you ordered your metal tank yet?

 

[john zibell]

Yes there must be one. The plastic tanks on the new bikes seem to withstand ethanol OK, or at least without major issues.

 

[Amboman]

You could always line it with Caswell Epoxy Gas Tank Sealer: http://www.caswellplating.com/aids/epoxygas.htm .
Easiest to apply and most durable sealer I've ever used. Works on metal, plastic and fiberglass tanks.

 

[geodoc]

Maybe eventually. For now:

http://pure-gas.org

You could always line it with Caswell Epoxy Gas Tank Sealer: http://www.caswellplating.com/aids/epoxygas.htm .
Easiest to apply and most durable sealer I've ever used. Works on metal, plastic and fiberglass tanks.

 

[DanPez]

Here in Quebec you can get 87, 89, and 91 AKI (91, 93 and 95 RON) octane fuels or even 94 AKI (98 RON)
at any Petro-Canada outlets ..... and if I'm not mistaken some Sunoco stations in Ontario have the 94 AKI also.
Used Ultramar 91 on my Stelvio, once or twice, plastic tank.... no issues. (Injection allthough inch: )
The lemon runs well with 91 (PHF36s) metal tank.

If ethanol blends are supplied by the station there labeled / identified at the pumps.

 

[Chris R]

Hi George,
Well that's a new one - I am a bit amazed that ethanol dissolves polyester. God knows what nasties are now coating the innards of your carbs.

I forgot you are an aero guy so pardon the remark. Given that Marvel Mystery Oil was invented sometime in the twenties I can't think it is anything particularly special - as you say some oil and some solvents.

I can vouch somewhat for Caswell's epoxy - I used it on my Falcone and it seems like good stuff - it seems to have the right amount of flexibility and 'thixotropicness'. I will tell you in twenty years if it is really good.

Glad you figured it out!

Ta,