Another Slow Jet Question

[Stratnick]

I have my carbs out and it has #35 slow jets and #100 main jets, which, by the way, are crusty and covered with a layer of varnish. I have done a lot of reading on #38 slows and I am leaning toward replacing the 35s with 38s. My I/S has what I believe is a Cobra exhaust system with custom tips on the back. For those who have installed 38s, how did they change how your Valk runs? I don't want to go to all this trouble only to regret changing to larger jets. Thank you all in advance for your help!

[salty1]

I run Cobra 6 into 6 exhaust with stock jets and a K&N air filter. Runs like a scalded dog. If you put in the larger jets expect your gas mileage to fall off. Might perform better.?

[John U.]

I'm running 38s in two bikes. They run better and after readjusting the pilot screws to 1 3/4 turns out (and the ECT mod) my mileage is 36 to 40 generally. That's with stock pipes and stock air filter though.

[John Schmidt]

They don't really affect your overall mileage, maybe a little bit around town if you have a tendency to twist the wrist. Your butt dyno might feel a slight improvement in bottom end grunt but that's open for discussion. It mainly gives better protection from buildup due to the corn liquor we now find in our fuel. In the end, if you ride a lot you won't have a problem with the #35. If it sits for extended periods at times...different story, seems to gum up the works. Due to extenuating circumstances, mine will sometimes sit for a week or two so I changed them out for #38. Runs fine, adjusted the pilots and noticed no real change in mileage.

Your results may differ! 

[BonS]

The big difference for me, and my IS, is reliability & torque when starting from a stop with light throttle. The 35's were a bit of a guessing game between a gentle smooth pull away and a sudden stall. The 38's give me a margin of reliability and safety that I enjoy.

[Ricky-D]

Changing out the idle jets from 35's to 38's will definitely affect the gas mileage.

Adjusting the idle screw will only have an affect on 1/4 of the whole idle circuit which isn't much and so you cannot get it back to about normal with that adjustment. You will use more gas.

The evidence is in most all comments made after changing out the jets. Namely: "I don't have to use the choke anymore."  This makes sense since now the motor is seeing a more gasoline enriched idle mixture.

The varnishing effect is remembering how, after a carburetor sits for long periods of time, evaporation of the volatile elements of the gasoline leave the remaining components to coat and dry within the carburetor float bowl and we call that "varnish".
That is not what happens with ethanol enriched gasoline. The deposits you find in this kind of gasoline are organic compounds formed because of the oxygen rich mixture now present in the gasoline. Some are actually organisms that can multiply and grow in the gasoline and which can really cause a mess when the gasoline is undisturbed and allowed to sit for a time where the gasoline can actually start to separate and form layers of different composition.

This is the stuff you find in the bottom of the float bowls and clogging up the carburetors. No amount of screens and filters can alleviate this problem.

The best proactive program is doing what you already are doing. Adding additives to the gasoline.

As ethanol enriched gasoline becomes more mainstream I am sure we will see better products coming on the market to address this pain in the ass problem.

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[John Schmidt]

Generally speaking, you're correct re. mileage. My experience over the past five years since I installed the #38's has been as I commented earlier....low speed in-town driving caused a slight drop in mpg. Before/after mileage if I run a full tank in town, there was roughly a 2mpg drop. But at highway speeds on long runs, I've seen no change. Naturally there will be variations from tank to tank, but overall through an entire trip I just don't see it. In town I pay no attention to mileage, a person's driving habits in traffic has the major impact on that, but on the open highway I just set the cruise control and let it roll. There's no on/off the throttle which even the best of riders will tend to do w/o a cruise.

There is the stated added benefit of easier starting and less use of the choke in cooler weather. And, I still run a can of bearcat pee through it about once a month....just for good measure. A lot of riders set the pilots at something less than two full turns out, yet I get my best overall performance with mine set right on two turns out. To each, their own!

[BonS]

Just to stir the pot a little more - Moving from 35's to 38's increases the total (main's + slo's) jet area about 2%. However, this does not translate into a 2% increase in fuel consumption. This is in part due to the adjustment of the idle air screw and in part because the engine was too lean to start with in the slow speed circuits to satisfy EPA emission requirements when manufactured. The slow speed circuits begin their life below a perfect stoichiometric ratio so bumping up the slow jets doesn't 100% directly translate in to additional fuel consumption. A full 2% hit translates into a 0.7 mpg loss and the real world hit is more likely closer to 1% (a guesstimate) and will be more like 0.3 mpg loss.

[R J]

I must be one of the lucky ones.    Still have the OEM jets, slow circuit, with 242K for mileage.    1st few years the bike never set long enough for the engine to get cold.    Now since my health has gone to hell and I'm not riding MGM, I still do not have a ton of varnishing in the carbs like everyone else claims.

I run ethanol 100% of the time unless I'm out of state and can't get it.   NO firkin problems with ethanol.......   The past 2 years MGM has not made more than 1,500 miles, 659 to be exact.    My son and my daughter have put all those miles on it.   I did ride Bitch with the son last fall, and the old boy had all the balls it ever had.  NO stumble, pulls like a scalded dog in 5th from 25 MPH on up to when ya back off of it.

Yes, he does get a full can of SeaFoam every other tank full, and one if going into winter storage.    Still use the choke as required, and it will start when the temperature is 10 below zero outside in a UNheated garage.  NO, I do not drain the carb bowls in the winter.    I'd like a explanation, why I have no trouble and everyone else has to sheet bricks and jump through hoops to keep their bike running right.   

[valkpete]

I don't understand either. I've had my girl for 6 years, every winter she goes in the shed, shut the petcock (stock unit never replaced or repaired) off and run the carbs dry, cover her lovingly, come out in March and turn the fuel start her up and ride all year with no problems. Change oil and filter after first ride. Then regular service according to the manual by mileage. I have been a mechanic for many years and a Honda tech for 12 yrs. I think it's all the junk you all put in your fuel tank. Honda does not reccomend any additives fuel or oil. Remember carb cleaner is toulene one of the most potent paint thinners out there, and is not good for rubber. Just my 2 cents.

[Ricky-D]

Just to stir the pot a little more - Moving from 35's to 38's increases the total (main's + slo's) jet area about 2%. However, this does not translate into a 2% increase in fuel consumption. This is in part due to the adjustment of the idle air screw and in part because the engine was too lean to start with in the slow speed circuits to satisfy EPA emission requirements when manufactured. The slow speed circuits begin their life below a perfect stoichiometric ratio so bumping up the slow jets doesn't 100% directly translate in to additional fuel consumption. A full 2% hit translates into a 0.7 mpg loss and the real world hit is more likely closer to 1% (a guesstimate) and will be more like 0.3 mpg loss.

Stirring further, the issue of how lean/rich the motor is/was has nothing to do with mpg figures with a change of jet size.
I agree with you that the change in the mpg figures would be small but it must at least be noted that the idle circuit is always in play while the main is not so much. So throwing everything in the pot in equal consideration is faulty.
Again, the loss of mpg would be small, but there absolutely would be a loss of mpg with a change to larger idle jets.
Whether or not the modification would result in an improvement or degradation is a determination that should be left to the individual rider.

***

[BonS]

All I'm saying is that the mpg hit with 38's is small no matter how you approach it and is borne out by the countless Valkyrie riders that have done it.