Mikuni Hsr 42 Carburetor Ez Kit

OK, I need some definitive input from a real mech-tech - will this carb be a good choice on my '99 FLHR TC88, given that I routinely go through major altitude shifts (sea level to 10Kft, garaged at 4Kft). I have the stock (but drilled) CV now w/high flow air cleaner, SE slip-ons but no other mods. Direct Parts has a GREAT deal on this kit now, so I'd appreciate a timely response. Making a 2000 mile run at the end of the month, too, so the clock is ticking......thanks in advance!

Loved it

Not sure about the altitude issues, but I had it on a 2001 FXD with the yost power tube, Ness Big Sucker, and Hooker Stepped Tuned pipes. Better throttle response, power and control. Not even worth comparing it to the CV with dynoJet kit I replaced.

The CV carb is better at adjusting for altitude. They are even used on light airplanes. I'd stick with a CV carb but go with a company like Woods performance or Dakota Kid Carbs to modify your CV for better running. I have the Dakota Kid work done on my carb. They bore the throat from the stock taper of 40mm - 38mm to a smooth bore 42mm and rework the fuel circuits. Transition is much smoother now and no farts/sneezes back through the carb.

In either service, you tell them what your build is and your carb will be jetted close and ready to run, right out of the box.

http://www.woodcarbs.com/

http://www.dakotakidcarbs.com/

Yeah, I read ya. Deathwind...everyone says they love it but no one tells me about the altitude issue. Am hoping that it will do OK if tuned for my home range of 4Kft, but need to be sure. I don't want crappy performance when I need mountain-climbing power. Only guy I know here that runs a Mik is a on a fancy sled that he only rides from bar to cathouse to home. Need a better review than that (and a more sober one, too).

Seahag - nice links, and unless I hear different from DP I'll probably use the CV rework route. Thanks for your input.

Yea, couldn't help there

highest I went with this bike was in Italy (1500-2000ft), then transfered to Greece, no altitude there, then back to the states. Since returning I sold the FXD before any long trips north, and even then the altitude would have only been 3000-3500. Other than that I loved it. I think that cost will be the factor here. Theres also the Thunderjet that is supposed to help at various altitudes and can be added to a reworked CV, but I can't find much documentation or reviews on it, so I have no clue if its good or not. Sorry I couldn't help more.

Ride Safe

The acronym CV really does say it all in this case. A CV or Constant Velocity carburetor works on a demand basis maintaining the velocity of the incoming air regardless of the throttle blade (butterfly) position. This is why you can get away with whacking the throttle wide open at low RPM and not bog unlike an S&S or even a Mikuni. The CV will only flow what the engine is demanding at the time. As demand increases, more incoming air is pulled into the slot at the top of the carb inlet. The outlet is much smaller and is beyond the throttle blade so it accelerates the air flow on the exit end. As the air fills the chamber, it pushes up on the diaphragm causing the slide to raise..raising the needle, adding more fuel. As the throttle is closed, air flow and demand lowers decreasing air pressure in the chamber and the spring pushes the slide back down. The bleed hole in the bottom of the piston and tension of the slide spring helps determine how fast the slide reacts to pressure (demand) changes. It is a common mistake to call the slide a "vacuum" slide when in reality it is a pressure slide.

A CV carburetor will work better than a butterfly type when riding in widely varying terrain. The common issue with any carbureted bike is the idle circuit. If you go from 2,500' to 12,000 and back your idle and off idle performance will change significantly. I used our own CP005 idle mixture screw to adjust the idle mixture easily when we were at drastically different altitudes than where we started from.

The other circuits, transition, needle, main jet will all act in basically the same way as a CV type does. The main difference is that a CV will be smoother when overly rich than a Mikuni will because the slide only raises based on demand.

EFI systems do not suffer the altitude blues of carbs and that is one major advantage they have.

BTW, Dakota Kid uses our products and we have heard nothing but good reports about them and their work.

CD - Thanks. Dakota Kid's got some business coming. But I'm sure he'll have suggestions for other improvements that you carry.

I've got a Mik HSR 42 on my scoot, been all over the southern states and even up in some of the central areas without any major tuning problems.

bikerjim1 - appreciate your input. If I still lived in Pensacola I'd probably jump on the 42 and be real happy, but it's a different world when ya cross mountain passes that "dip" to 10,000ft. Thin air is hard enough on people, and is a bear on a finally tuned carb set for lower altitudes.

Keep the seat side up.....

Got 'cha.

Here is some information DK doesn't advertise on their site (I don't think). If you request it, they can put a deposit on your credit card and ship you off one of their completed carbs immediately. Then when you have completed the swap, you mail your carburator back in for a core exchange and have your deposit returned.

My father in law, went this route when we swapped his carb (he went DK after he saw how nice the work was on mine) which was nice as there was no downtime.

As CD said, they use the knurled pilot adjusting screw, so you can reach down and make small adjustments, instead of carrying a small blade screwdriver everywhere.

I just talked to DK on the phone and the man said he's loaded up with junk carbs now and wants me to send mine first. FYI, he wanted me to include an emulsion tube with it 'cuz I had the Thunderjet drill job done previously. I can't afford the downtime now, so I'll have to wait - but it does sound like the way to go for non-EFI bikes that ride the mountains.

Speaking Of The 42 Mm

Only just last night I put one on my 1991 FXR P. This is my 2 nd FXR that I put a 42 MM on. Everyone has there own feeling about oil, carbs and so on.
In all the years that I have been using the Mikuni 42 MM carb. I have never had any problems with it. I have gone through many differant alttitudes from sea level on P.C.H. All the way up highway 78 to the Hideaway Biker Bar. Then up over the mountains with chaps and full gear on. Then going down the mountain into Palm Desert Calif. stripping down to my tank top.
The Mikuni has never failed me or let me down.
My suggestion to you would be get it on as soon as you can. Then feel it out and make sure you have the great response from it, without any lag. I like i said just put mine on last night and didn't have to do a thing to it except adjust the idle a tad. So I guess you can tell which way I think you should go.
Gumby, I am going to assume this was accidental SPAM? Please read the FAQ regarding SPAM before posting again. This is the FAQ you "read" and agreed to when signing up.
http://biketalk.directparts.com/faq.php?faq=vb_faq#faq_new_faq_item_spam


Hope you have a great run. Enjoy Enjoy Enjoy, gumby321

gumby321 - thanks for the input. Not sure of the altitude shift's that you had, though.

By the way, not to be mean or anything, but I have to point out that the company that sponsors this forum actually sells the HSR42 for $14 LESS than what you paid. That's why I started thinking about getting one in the first place.

Here's the link:
https://www.directparts.com/cgi-bin/dp.store

I'd suggest everyone cruising these forums check out the Direct Parts e-store. Not the best format (sorry CD), but I see a lot of items that interest me that are at great prices - on things that I might actually buy, not just day-glo T-shirts! Haven't bought anything from 'em yet, but I expect to. Just need to build up some $$ for new pipes.

No problem about being mean.

I would rather be told then not told. I am very new to all of this. I am talking about the computer and working on my own bike. So please everyone forgive me for my mistakes. Just remember I am as green as green can get when it comes to these new electronics. i couldn't tell you what a MP3 is or what it does. I still have old 45's and albums. I do have a cd player too. Thats as far as I go though.
Now that I know that this site not only has fine people here, you can find cheap good parts. I will figure out how to get to them tonight for sure.

As far as my altitudes from sea level on P.C.H. then going up either hwy# 74 or # 78 I think. It has to be atleast over 7 thousand feet if not more.
It felt like I went through 4 weather zones. Thats how differant the temps. were. If anyone out there knows the biker stop called The Hideout inbetween the beach near San Diego. Then following hwy#74 up and over the mountain.
You will come out and head downhill into the town of Palm Desert Calif. it's one of the better rides in that area. You have all types of roads. From city then mostly mountain roads that are just the best to ride through.
Then you can spend the night in the town of Palm Springs or Palm Desert. There are many friendly bikers in both of those towns. If your not from the area, they will make you feel like you are.
There is a run to the desert every year. I believe it is in the month of Oct.
Go to it, it is peaceful and there are many places to go riding.
I am off to find some parts here now. I just picked up another FXR. I had to sell my last one to buy a house here in Las Vegas. I hated to do it but it was well worth it in the end. Now I have to fix and add parts that make me comfortable. I installed my forward controls and that Mikuni carb. that started this whole conversation. I must say I do love it and never had any problems with my last one. Thats why I went back to it again. I did alot of riding. All over the state of calif. down to Mexico for the Baja 250. Then up to northern Calif. to the redwoods. Mind you all this was not in one week. My point being is that the carb. was great in all those situations. So I hope this little rant helps in making your mind up. Like I said never a problem at all with the mikuni. So enjoy no matter which one you buy. Just be careful. PEACE

Hi gumby321, I was wondering if you might know if the Mikuni could be the cause of a 3200 to 4000 irregular power? It does not happen all the time but, seems like only in high gear when it would be under a higher load. The tech even bounces around so, I end up choosing to ride at 4000 RPM and that just ain't legal. I cleaned it, and if I crank the bike without doing anything first, and then crank it again giving it a little throttle, starts fine. It floods instantly when cold otherwise. I had a few other bikes before and this one is the most finicky starting bike that was not actually broken.
Any ideas on the 3200 to 4000 intermittent power issue?
Honestly kinda feels like a bad points issue but, seems it ok at 4000 + RPM.

Red Rider,

I have a 42 or 45 Mikuni on a 99 roadglide. 95 " big bore. I live in Alabama. Rode the bike from Al out thru Texas, NM, Utah, Idaho,over Yellowstone out to Cody Wy, over Beartooth Pass @ 10,000' and into RedLodge Mt. on into Billings, back across SD, Iowa, Tennesse and back to Al. I had no issues with the carb. I have ridden evry stste east of the Mis.River with no issues with the carb. I have a Mikuni 45 on my 1990 EGlide 107" ultima and i have had no issues with it.

later.....................

Thanks, Paco, but at this point I'm sticking with the stock 40mm CV. I can see why you'd need a bigger flow with your engine, though.