Carb Tuning Help

[D0wn5h1ft]

So I'm having a bit of a problem. I changed out my 4 to 1 exhaust for a 4-2 exhaust and I'm having some bogging down issues. I have never tuned carbs before and I was wondering what might be my issue. If I'm sitting in 4th gear around ~2500 rpms and I open up the throttle a lot I notice a huge lack of power and the engine sounds like it's struggling. I had this issue a bit with the 4 to 1 exhaust but it has gotten significantly worse with the new exhaust. I guess I have a few questions [yes the butterflies have been bench synced] [Also, I have pod filters on]:

-Does a new exhaust require carb tuning? (I assume yes)

-If I have to tune my carb, where should I start? Should I start with the idle screws? And would the idle screw mixture be the main issue with this lack of power I'm noticing?

-I noticed the #3 spark plug is a light grey color, does that mean it's running too lean? And if so how do I fix it?

-Do I really need to get new jets or is there some tuning I can do to see if the ones I have will work?

-Which jets do you think I would need to change out if any? (Mains, Pilot, etc)

I think the float levels are fine because my high end power is great (>5k rpm). The jets aren't clogged because I just triple cleaned the carb. I guess I just need some help on where to start. I have read the guides on here but I'm not really sure which ones apply to the issues I'm having.

[motoman]

So I'm having a bit of a problem. I changed out my 4 to 1 exhaust for a 4-2 exhaust and I'm having some bogging down issues. I have never tuned carbs before and I was wondering what might be my issue. If I'm sitting in 4th gear around ~2500 rpms and I open up the throttle a lot I notice a huge lack of power and the engine sounds like it's struggling. I had this issue a bit with the 4 to 1 exhaust but it has gotten significantly worse with the new exhaust. I guess I have a few questions [yes the butterflies have been bench synced] [Also, I have pod filters on]:

-Does a new exhaust require carb tuning? (I assume yes)

-If I have to tune my carb, where should I start? Should I start with the idle screws? And would the idle screw mixture be the main issue with this lack of power I'm noticing?

-I noticed the #3 spark plug is a light grey color, does that mean it's running too lean? And if so how do I fix it?

-Do I really need to get new jets or is there some tuning I can do to see if the ones I have will work?

-Which jets do you think I would need to change out if any? (Mains, Pilot, etc)

I think the float levels are fine because my high end power is great (>5k rpm). The jets aren't clogged because I just triple cleaned the carb. I guess I just need some help on where to start. I have read the guides on here but I'm not really sure which ones apply to the issues I'm having.

Good on you going to a 4into2 exhaust. Makes it a bit easier to tune to run well all rpm ranges. Having said that, I would check ALL jets including the air jet on back of carb bell to see if they are stock for THAT year carbs. Haven't seen where you said if air intake is stock or not....also makes adifference in jetting, and becomes a balancing act if not. Either way, starting with stock jetting(Genuine Mikuni) as a baseline is what needs to be done first. Having never had anything but stock myself, betting setting up stock as a baseline will have bike runnin' fairly close to correct with the 4into2 set-up, and make it easier to make slight changes from there, and eliminate alot of just guessing. Main jets a bit on the large side would initially be suspect, but until you can confirm their size AND brand, just a guess at this point. Get that back all correct, THEN a correctly done sync and idle mixture setting will eliminate alot of head scratching for you AND here concerning questions and helpful answers.

[donebysunday]

So I'm having a bit of a problem. I changed out my 4 to 1 exhaust for a 4-2 exhaust and I'm having some bogging down issues. I have never tuned carbs before and I was wondering what might be my issue. If I'm sitting in 4th gear around ~2500 rpms and I open up the throttle a lot I notice a huge lack of power and the engine sounds like it's struggling. I had this issue a bit with the 4 to 1 exhaust but it has gotten significantly worse with the new exhaust. I guess I have a few questions [yes the butterflies have been bench synced] [Also, I have pod filters on]:

-Does a new exhaust require carb tuning? (I assume yes)

-If I have to tune my carb, where should I start? Should I start with the idle screws? And would the idle screw mixture be the main issue with this lack of power I'm noticing?

-I noticed the #3 spark plug is a light grey color, does that mean it's running too lean? And if so how do I fix it?

-Do I really need to get new jets or is there some tuning I can do to see if the ones I have will work?

-Which jets do you think I would need to change out if any? (Mains, Pilot, etc)

I think the float levels are fine because my high end power is great (>5k rpm). The jets aren't clogged because I just triple cleaned the carb. I guess I just need some help on where to start. I have read the guides on here but I'm not really sure which ones apply to the issues I'm having.

What exhaust did you go to ?
What air filter/s are you using ?
You had this problem before with the 4-1 and it's worse with the 4-2.

So the engine is able the exhale even better than it was with the 4-1.

Can you get it to red line ?

I would say larger mains, I'd like to hear more please.

[D0wn5h1ft]

I am using pod filters, in gear it struggles to get above 5k rpms under load (new issue with new exhaust), dual Mac exhaust. Never really had this issue before. Mid range power band is still really good. Noticed that my idle was significantly lower with the new exhaust (with the same idle setting) it was around 1500 with the old exhaust and now it is ~900-1000.

[TopCatGr58]

Hey there Downshift,

I just researched, reviewed your other 20 posts. We really do need lots of more info about the bike before we can make intelligent suggestions regarding tuning and such. SO...to recap for folks from what you've posted in the past:

Bike is relatively new to you(78E), PO had done Big bore kit, and Dynatek coils.

You rebuilt carbs...but never posted about what jet sizes you had, or whether you used any carb "kits", or just cleaned the parts and put them back in...so we don't know if you have genuine Mikuni or the crappy K&L brand, etc?? Also, did you SOAK the carb bodies in caustic carb DIP cleaner=damages the butterfly shaft seals, or just use carb cleaner spray and such?

You've also performed the Dremel gear fix...no small task in itself!!! Cudos.

You haven't stated whether you have checked the PU coil wires for faults, breaks, etc.. Also verified that you are getting power to all cylinders...spritzed water on the headers to ensure that all 4 sizzle after it's warmed up.

The photo you have posted is from afar...so we can see the PODs, but can't see if you've done any version of the velocity stack mounting mod for them...which can help increase low rpm throttle response, and eliminate air flow restriction that the cheap EMGO brand pods mounting lip can cause when directly on the carbs.

Now, although folks state that these engines when properly tuned and such will/should pull from 2K rpm on up in essentially any gear....starting at 2K is still quite SLOW and close to lugging rpm when in the higher gears..IMHO! These engines do have good torque, but they aren't HARLEYS, they like and need to be running a bit faster for good throttle response in the higher gears....I rarely let mine run below 3k in ANY GEAR!

T.C.

[petejw]

id recheck your fuel heights
and that you have them set correctly for the model carbs
you have fitted. (theres 2 different settings for older and later model carbs)
sounds like u may have them set on the richer side of things,
before messing around with jets.

[motoman]

What exhaust did you go to ?
What air filter/s are you using ?
You had this problem before with the 4-1 and it's worse with the 4-2.

So the engine is able the exhale even better than it was with the 4-1.

Can you get it to red line ?

I would say larger mains, I'd like to hear more please.

Mains are fine if pulling hard to redline with no slowing at tach. If anything, a step lower may or may not be needed, or as petejw suggested, double check that float height before screwin' with main jets......remember, one change at atime......test before moving to different change.

[D0wn5h1ft]

So in an attempt to give you guys more information here are my spark plugs (counting how you're supposed to; left to right):

Cylinder #1


Cylinder #2


Cyilnder #3


Cylinder #4


These plugs were brand new when I put the dynatek coils in (a few weeks ago) so they are fairly indicative of how the bike has been running. I'm not sure exactly what they'll tell you but it looks like the inside two cylinders are running a bit lean (possibly something to do with the points or ignition?).

Also, in an attempt to narrow this down a little more I remove the carbs, bench synced them (they were pretty far off...i'm not sure how since I just did this a month ago), and tuned the idle mixture. Took her out for a spin and she's doing a lot better but still not there. Getting that bogging down sound if I'm sitting at 2500-3000 rpms and I open up the throttle a lot; aka poor throttle response.

I also tested the high side rpms and I get a smooth and steady increase in rpms from 3k to 5k rpms and then it slows down substantially and then crawls up to redline slowly. I'm thinking, from reading all the available material on this site again, I possibly need a larger pilot and main (?).

To answer some of the questions posted:

-When I "rebuilt" the carbs I took them apart and cleaned it out with carb cleaner since they were in pretty good shape when I got them; no need for a bucket of cleaner

-I haven't a clue how to check which set of jets are in there. My assumption (about 80% sure) is that the PO never rejetted the carbs when he put the pods on so I'm assuming stock jet sizes. From the condition he left the bike in when I got it doesn't seem to me that he'd go through that sort of care.

-Don't give me too much credit on that dremel fix...I have to go back in there this weekend and put the snorkel gear on to regrind those 4th gear slots. [or replace the whole trans with the parts bike I have but I really don't want to do that since I'm looking to restore it this winter ]

-The bike isn't misfiring at all, that I'm for certain. All pipes are nice and hot and not missing a beat at idle

-As far as the velocity stack mounting mod, I haven't heard of that one before. Is there some resource you can point me to?

[IanDMacDonald]

Hell yeah! You got yourself some richness going on there brother! Either your float height is off, mixture screws are out too much, or your jets are too large. Like Motoman said "one thing at a time". When you start messing with all different circuits at the same time, you'll never know what's going on. Take a step back, figure out what is good, and what is bad.

[IanDMacDonald]

Set your float height and jets to stock numbers and then see what is going on. Also, turn screws all the way in till soft seat then out three turns and sync. Clean the plugs and see how they look after.

[D0wn5h1ft]

Hell yeah! You got yourself some richness going on there brother! Either your float height is off, mixture screws are out too much, or your jets are too large. Like Motoman said "one thing at a time". When you start messing with all different circuits at the same time, you'll never know what's going on. Take a step back, figure out what is good, and what is bad.

What is up with the two white plugs then? Isn't that indicative of a lean mixture? If so why would the inside cylinders be lean and the outside ones rich? I assume to do the poorly synced carbs?

[petejw]

yeah, those plugs are way rich,
the 3rd pic looks best but its still rich,

check this site out for reading plugs
https://www.google.com.au/search?q=r...08%3B779%3B600

jat, if u have an air compressor and air gun,
look up home made soda blaster to clean the plugs,
itl save you a heap on buying new plugs.

[petejw]

no, theyre still running rich,
have a look at the link I just posted,
Cpl of reasons why they are different,
mixture screws could be set incorrectly,
the sync could be out,
float levels not set correctly,
take the carbs off and recheck everything,
also check if the slide needles are set correctly if
theyre adjustable, not sure what carbs u are running.

[motoman]

Slow pullin on the top-end is my first clue to too rich in the mains, float levels too high, or metering rods set in higher clip position. Looks to be the same effect at the lower end too by what you are reporting. BTW, no points in these bikes. They're a bit old, but not ancient. The plugs show normal for their location. Two center cyl. run a bit hotter, and plugs show that based on location. The good news is the two outer plugs are identical and the two center are identical. That tells me float levels are pretty dead-on all the same and firing of plugs is all good. For not actually having done a CORRECT sync, pretty good I must say, even though a bit rich (which could be from idle circuit cruisin back to house). That possibly being the case, not being there not knowing exactly how and where ridin before plug removal, and if having the matching year early carbs, I'd suggest removing the slides(under chrome carb top covers), remove the needles(read tech tips on procedure of removal and installation), RAISE the clip on the metering rods one position which drops the needles. Pay special attention and keep each slide with THAT carb it came from. Porclien looks good as if was run at high enough rpm in the main circuit, but at the lower rpm, maybe towards end of ride in the lower rpm range metal threaded ring all the way down to inside base was blackening up. One change at a time IS critical to start eliminating the problem! No offense intended, but the points question tells me your not very savvy at this point, so don't be afraid to ask. The only dumb question is the one not asked here FIRST, before proceeding!

[TADracer]

"when I put the dynatek coils in (a few weeks ago)"

Which Dynatek coils did you install? If they are the 3 ohm coils (Green ones) and you did not bypass the ballast resistor on your 78E then you will run exactly the way your plugs are reading due to a very weak spark.

If you do not have 1.5 ohm coils then you must bypass the resistor if you have not done so already.