Should I rejet?

[EZRider76]

So tonight I tore my carb apart, basically because I was bored and had never attempted a carb tear down before. I was also curious about all these people talking about main jet sizes and pilot sizes. :-/ Now, I'll admit openly, I carb-tarded....but I'm learning, very slowly. I did a bunch of reading, and I'm still clueless...so now I'm asking the questions. And of course, I graciously and humbly thank you for your knowledge and wisdom. I:I

So, I have a 28mm Mikuni VM. Here she is:

When I did some disassembly tonight, I saw that I have a #150 Main Jet...and I couldn't read what I am assuming is the Pilot. I will take pics tomorrow of it cracked open again, I just want to know what I'm tinkering with. Also, seeing how I live at 1808' Elevation, and ride between that and probably 2000', should I rejet? Take me to carb school fellas, just go slow and be gentle with the terminology...lay the sarcasm on as thick as you like.

 

[Awk08]

i'm not too versed in mikuni jetting, besides the 26mm stock ones, which come stock with a 230 main
i could be wrong but i'd assume a 28mm should require a bigger main than the stock carb ?

the stock carb on my black bike requires a 300 main for the trinity pipe, vf3's and open airbox


and as you rise in elevation, your jetting will need to be leaner, i run the same elevations as you
sea level requires richer jetting than our 2000'
mile high denver would require leaner jetting

but that 150 sounds too small to me for a mikuni

 

[EZRider76]

i'm not too versed in mikuni jetting, besides the 26mm stock ones, which come stock with a 230 main
i could be wrong but i'd assume a 28mm should require a bigger main than the stock carb ?

the stock carb on my black bike requires a 300 main for the trinity pipe, vf3's and open airbox


and as you rise in elevation, your jetting will need to be leaner, i run the same elevations as you
sea level requires richer jetting than our 2000'
mile high denver would require leaner jetting

but that 150 sounds too small to me for a mikuni

Ok, remember way back a couple weeks ago, when I was inquiring about that open port on the carb? When I rode the Blaster around the yard, the thing screamed...at least it felt like it. I since have blocked off that port and plugged the fitting for the oil injection. When I got the cable situated and fired it up the other night, it ran for maybe a minute then stalled. After about 20 kicks, 2 minute pause and 5 more kicks, it fired up again, idled for 10-15 secs, revved up and then stalled. This happened a few more times, even when I tried feathering the throttle, it would just die...even WFO, so then I started looking for an air leak. I replaced the intake boot tonight, as that was starting to dry rot and had cuts in it, just not all the way thru. Could the stalling be because my main is way under size? Does this mean it's just not getting enough fuel?

 

[Awk08]

the main has nothing at all to do with starting or idle
the float setting, pilot jet and airscrew are what the bike uses to start and idle
the needle comes into play about 1/4 throttle to 3/4 throttle when the main jet kicks in also to full throttle

get us float height, pilot #, airscrew setting and needle clip position and we'll go from there

 

[EZRider76]

the main has nothing at all to do with starting or idle
the float setting, pilot jet and airscrew are what the bike uses to start and idle
the needle comes into play about 1/4 throttle to 3/4 throttle when the main jet kicks in also to full throttle

get us float height, pilot #, airscrew setting and needle clip position and we'll go from there

I will see about the pilot #, it was pretty hard to read. To measure the float height, I need that "cork" with the tube on it right? And just to refresh my memory, which is the airscrew? Is that what is commonly known as the idle screw?

 

[Awk08]

no, the airscrew and idle screw are 2 seperate screws and perform 2 different tasks

the airscrew usually starts set at 1.5 turns out, it adjusts air to the pilot jet circut, and it's final setting helps determine if you have the correct pilot jet
the airscrew gets adjusted to where the engine idles the highest, starting at 1.5 turns out, adjust it 1/2 turns and give it 20-30 seconds for the engine to react to that change
turn it in to 1/2 turn, and out to 3+ turns, and keep track of where your at, the setting that it idles the highest, tells the tale
under a 1/2 turn = larger pilot
over 2-1/2 turns = smaller pilot

then it can be played with at 1/8th turns to acheive good clean crisp revs to 1/2 throttle

once you acheive high idle, the idle screw is used to adjust the rpm's to your desired idle,
that is it's only purpose

here's some good homework for ya, read, re-read, and re-read again until you understand each circut of your carb, and it's good you have it out on the table, as you can sit and read, then locate and practice each different task needed to properly tune your carb, although no results while on the table, it'll teach you what needs done once installed

BTW......there will be a pop quiz on friday morning, LOL........

http://www.blasterforum.com/do-yourself-20/jetting-101-everything-explained-1625/


you can use the cork/hose method if your float bowl has the removeable nut on the bottom, if not, connect the hose to the drain and open it holding the hose up beside the bowl ???

i do them like this, actually measuring the height, and i did not locate a measurement for your 28 mikuni ????

 

[EZRider76]

no, the airscrew and idle screw are 2 seperate screws and perform 2 different tasks

the airscrew usually starts set at 1.5 turns out, it adjusts air to the pilot jet circut, and it's final setting helps determine if you have the correct pilot jet
the airscrew gets adjusted to where the engine idles the highest, starting at 1.5 turns out, adjust it 1/2 turns and give it 20-30 seconds for the engine to react to that change
turn it in to 1/2 turn, and out to 3+ turns, and keep track of where your at, the setting that it idles the highest, tells the tale
under a 1/2 turn = larger pilot
over 2-1/2 turns = smaller pilot

then it can be played with at 1/8th turns to acheive good clean crisp revs to 1/2 throttle

once you acheive high idle, the idle screw is used to adjust the rpm's to your desired idle,
that is it's only purpose

here's some good homework for ya, read, re-read, and re-read again until you understand each circut of your carb, and it's good you have it out on the table, as you can sit and read, then locate and practice each different task needed to properly tune your carb, although no results while on the table, it'll teach you what needs done once installed

BTW......there will be a pop quiz on friday morning, LOL........

http://www.blasterforum.com/do-yourself-20/jetting-101-everything-explained-1625/


you can use the cork/hose method if your float bowl has the removeable nut on the bottom, if not, connect the hose to the drain and open it holding the hose up beside the bowl ???

i do them like this, actually measuring the height, and i did not locate a measurement for your 28 mikuni ????

**scratching head** ok?!?! So, not only do I have to read, NOW there's gonna be a pop quiz?? Shut the front door...wait, it's not really a pop quiz if I know about it ahead of time. :-/

I kinda figured the air screw and idle screw were two different parts, but I just wanted to make sure. Now I just have to figure out what my air screw is on the carb...I think I know, but I'm not 100% and being at work now I can't see my pics.

Well, luckily my carb can drop a nut out the bottom, , so I think I'm gonna build me a tool. I:I I think before any of this though, I'm gonna hunt around and see if I can get a parts breakdown and maybe a manual of my carb. It sucks having to guess at this stuff, and then describe it, and the answers ya get in return are generalizations, mainly because there's no specificity (<--actual word, I looked it up).

I'll give you a shout in a couple days when I get this all worked out. I gotta get a new idle screw for the carb too. I don't know how or why, but it's bent. I tell ya, every little thing on this bike...EVERY little thing, needs to be looked at. X(

 

[Awk08]

i'm seeing 15-17mm float height for a mikuni vm 28 ??


https://cyclewareables.com/pages/mikuni_vm26_44mm_parts_diagram/mikuni26mm44mm.htm


complete manual
http://www.mikuni.com/pdf/vmmanual.pdf

 

[EZRider76]

i'm seeing 15-17mm float height for a mikuni vm 28 ??


https://cyclewareables.com/pages/mikuni_vm26_44mm_parts_diagram/mikuni26mm44mm.htm


complete manual
http://www.mikuni.com/pdf/vmmanual.pdf

I:I Sweet. Thanks. I found it last week when I was scrambling looking for the cap, I just had to refind it. I've already printed it. Funny thing though, that part number for the cap in this manual, both Motion Pro and Sudco/CarbPartsWarehouse, told me that it wouldn't fit my carb. :-/ No matter, I got that problem fixed. B)

 

[nd jat]

The 28 should jet close to the stock from my experience with mine. So the pilot should be the 23.5 I believe and 240 main for completely stock. 270-290 range with af pipe and airbox lid off.

 

[EZRider76]

The 28 should jet close to the stock from my experience with mine. So the pilot should be the 23.5 I believe and 240 main for completely stock. 270-290 range with af pipe and airbox lid off.

From memory, seems like the numbers I couldn't read on the pilot were 23.5. I'm gonna take it in the house tonight and tear it apart in there, better lighting...warmer I:I...and try to snap some pics. Main jet was definitely a #150 though. Seems to be quite a difference from your 240, or 270-290.

 

[EZRider76]

Ok, so, I have an announcement to make...figured out the idling and stalling issue. Can't believe this wasn't a suggestion...lmao. FUEL!!! The freaking thing was out of fuel. Bahahahhahaahhaaaa.

Also, I rechecked the numbers, and #150 Main and 52.8 Pilot...does that sound right for a Pilot #? I know I said I would have pictures, but once I figured out the stalling issue, I didn't want to take it back off again.

 

[Blaaster]

Do you have to put fuel in the tank?

I thought that would be the last resort.

What a cheap fix!

 

[mjgnslngr]

<<<Been there, done that... What are the results? did you change the main?

 

[Blaaster]

I just wonder how many times a mechanic has been called to help fix a motor that just needs fuel.

I will put my hands up and own up to chasing an electrical problem for an hour on a vehicle with an auto box, when the problem why it would not crank, was only that it was in drive.

Silly old fart, me!

 

[mjgnslngr]

i remember the first car i worked on fresh outta high school. 79 malibu 4dr with a 305 2brl. it was stumbling and blowing black soot out the tailpipe, flooding .i said to the boss "hey, looks like were gonna have to take the carb off and totally rebuild it" he comes over whacks it with a hammer. thing stopped chugging and the idle smoothed right out. he says " dont throw too much effort after foolishness kid!!!" lol still remember that.

 

[EZRider76]

<<<Been there, done that... What are the results? did you change the main?

I haven't changed the main yet, I wanna do a leakdown test, then if all is well a plug chop. Who knows, maybe with my set up, a #150 might be the trick....I doubt it, but first things first. No sense in toiling away at a minor thing when there could be something serious going on I don't know about.

Yes Blaaster, you have to put fuel in the tank...these American machines don't run on carbonated water ya know. Anyhow, they are like babies, ya gotta feed them. It is funny how the little things can be over looked. I wonder if that is why computer guys ask, "Is it plugged in?", "Did you push the power button?" and then they come up with those stupid words like PEBCAK, and say those funny codes like ID-10T....why can't they speak english. 8-|

 

[Awk08]

the postion of the airscrew that it idles the highest is the only way to confirm the proper pilot jet
if it idles the highest under 1/2 turn out = larger pilot
idles highest over 2-1/2 turns out = smaller pilot

btw...stock blaster pilot is 32.5, not 23 sumthin or other

and a plug chop is the only way to confirm the main jet, i'd throw a larger one in there to be safe, you cannot feel it frying the piston until it is too late
i'd try atleast a 250, or 290 to be really safe and work down
i know, i know, it's a pain in the azz, but must be done

http://www.blasterforum.com/do-yourself-20/how-plug-chop-38674/

 

[nboldman]

the postion of the airscrew that it idles the highest is the only way to confirm the proper pilot jet
if it idles the highest under 1/2 turn out = larger pilot
idles highest over 2-1/2 turns out = smaller pilot

btw...stock blaster pilot is 32.5, not 23 sumthin or other

and a plug chop is the only way to confirm the main jet, i'd throw a larger one in there to be safe, you cannot feel it frying the piston until it is too late
i'd try at leats a 250, or 290 to be really safe and work down
i know, i know, it's a pain in the azz, but must be done

http://www.blasterforum.com/do-yourself-20/how-plug-chop-38674/[/QUOTE/]

Listen to the man! I had the stock main jet in which is 230 and mine blew up after 4 hours of good riding.

 

[mjgnslngr]

What did the carb come off from originally? i think awks right, that still sounds small. i thought even the 28mm vm mikuni have simular style/sizing jettingas the stock 26vm blaster carbs, correct? so like a 270main? 32.5 pilot?