Topic: 750K1 consistent leanness....now with plug pics!

[cheftuskey121]

hey guys, been chasing a lean issue for quite some time. been checking all plugs a LOT lately, and I am consistently lean. I notice the engine being pretty hot. not getting any pops on accel or decel though. a little hesitation taking off from a stop unless I get the rpms to 4k first. it's hard to take off slowly. also crusing really slowly at 1/8 throttle or less makes the rpms kinda wander and not stay consistent. increasing rpm fixes it. I can ride the balls of this bike no problem but I dont want to goose it stoplight to stoplight, and I dont need need any highway tickets

 everything is stock and brand new OEM for a K1. except 341s. I did have 110 mains in there to compensate for the 341s but experienced popping at WOT. went to 120s and that issue is fixed. needle is in middle position which hondaman said on a K1 is actually rich...I'm not running rich according to plugs. I am starting to think its a fuel starvation issue causing leanness, more so the fuel level in the bowls. I have the honda 26mm float height tool, but when I pulled the bowls the other day and 3 of them just looked lower than they should be (the carb with the choke lever attached looked higher ie normal). I believe this also is causing a little idle chasing too.

so I guess I am curious where I should start? probably at the source yes? check that my petcock flow is right. then check the fuel lines. I have stock 5.5mm fuel lines that are routed stock and are a minimal short length not causing any crazy drops or such. no fuel filter. hard to see fuel flow because its black. I read it took someone 15 seconds to fill an 8oz cup with fuel from the petcock. I'll try that. then move to the floats. now lets say that for sure the heights are set correct, can the fuel level be too low? if the answer is no then I obviously have an issue there. the idle screws are set out 1ish turn on each, and am not too lean at idle.

I have put 1500 miles on it since getting it on the road, and it has been a blast. I probably answered all my questions already, just looking for any insight, guidance, or comments. all my tune up stuff is done except the sync. I have a morgan carbtune and want to use it but need to get this lean issue sorted first. if everything is stock it should run like it was meant to, thats my line of thinking at least. thanks for the wealth of knowledge here, I would not even have ANY line of thinking if it wasn't for you guys!

[Don R]

The float level is important, check it soon. You did say the stock  air filter and box is in place? I left the bottom of mine loose once and couldn't believe the difference.

[cheftuskey121]

The float level is important, check it soon. You did say the stock  air filter and box is in place? I left the bottom of mine loose once and couldn't believe the difference.

correct, the stock filter is in the box, and it is snug. will double check tomorrow though. I wanted to put a K&N filter in there but when I did it became WAY too lean and I could not even cruise at 1/8-1/8 throttle at all, it just choked there. tomorrow I will check the fuel flow and floats, and also check boots for any leaks, the carbs came off and went on the other day when I set the needle back to the middle position. the needle was previously lowered per hondamans recommendation to lean out the rich K1 mixture. perhaps something went awry when I had the carbs off. I'll post back with any results later

[bjbuchanan]

Move your needle clip position one step richer from where it is. I bet you it clears right up. The RPM isn't too important but throttle position is. But 4k~ rpm or so in first is right around that transition to 1/4 throttle incidentally. The fail with the k&n filter is a big indicator too. It made the leanness at that transition even worse.

I went through the same thing with my bike like 2 months ago. Screwed with pilot jets and mixture screw position til I finally just said screw it and moved the needle clip position and solved the issue

[cheftuskey121]

Move your needle clip position one step richer from where it is. I bet you it clears right up. The RPM isn't too important but throttle position is. But 4k~ rpm or so in first is right around that transition to 1/4 throttle incidentally. The fail with the k&n filter is a big indicator too. It made the leanness at that transition even worse.

I went through the same thing with my bike like 2 months ago. Screwed with pilot jets and mixture screw position til I finally just said screw it and moved the needle clip position and solved the issue

thanks for the insight bj! glad to hear it worked for you. I am an overthinker though so I am curious as to why its being lean in the first place when the K1 is supposed to be notoriously rich, and I am at stock settings. not saying raising that needle wont fix it....I probably will end up doing that! but just curious as to "if its stock WHY AINT IT WORKING"

[seanbarney41]

Yes, correct float height does not always result in a correct fuel level in the bowl.  Have you checked the fuel level in the bowls via the clear tube method?

[cheftuskey121]

Yes, correct float height does not always result in a correct fuel level in the bowl.  Have you checked the fuel level in the bowls via the clear tube method?

I have not, I don't know what that method is

[scottly]

hey guys, been chasing a lean issue for quite some time. been checking all plugs a LOT lately, and I am consistently lean. I notice the engine being pretty hot. not getting any pops on accel or decel though. a little hesitation taking off from a stop unless I get the rpms to 4k first. it's hard to take off slowly. also crusing really slowly at 1/8 throttle or less makes the rpms kinda wander and not stay consistent. increasing rpm fixes it.

Sounds like your running issues are more in the range of the idle jets, rather than the needles. Do verify the float bowl levels with the "clear tube" method. You insert a piece of clear vinyl tubing into the bowl drain hole, after removing the K1 drain plug, and use it as a spirit level. The search tool is your friend, but sometimes it helps to know what terms to search for.

[cheftuskey121]

hey guys, been chasing a lean issue for quite some time. been checking all plugs a LOT lately, and I am consistently lean. I notice the engine being pretty hot. not getting any pops on accel or decel though. a little hesitation taking off from a stop unless I get the rpms to 4k first. it's hard to take off slowly. also crusing really slowly at 1/8 throttle or less makes the rpms kinda wander and not stay consistent. increasing rpm fixes it.

Sounds like your running issues are more in the range of the idle jets, rather than the needles. Do verify the float bowl levels with the "clear tube" method. You insert a piece of clear vinyl tubing into the bowl drain hole, after removing the K1 drain plug, and use it as a spirit level. The search tool is your friend, but sometimes it helps to know what terms to search for.

thanks scottly. yes I love searching am reading up on it now. seems fairly simple. I'll have to check my idle jets but they were not clogged up before. haven't had any issues with dirty gas etc. when the carbs come off I instinctively check all the jets because I am a little too paranoid. just thinking about it makes me wonder how all 4 carb float tangs can be set the same yet 3 of them are low. maybe I boogered them when putting the bowls on. ok, too much thinking and theory and not enough sleeping and action. thanks for all the info. more reading to do and then testing tomorrow

[scottly]

just thinking about it makes me wonder how all 4 carb float tangs can be set the same yet 3 of them are low.

The springs in the float needles can vary widely, such that the "normal" method of mechanically setting the floats shows drastically different actual fuel levels in the bowls. The clear tube will show the true level.

[seanbarney41]

Yes, correct float height does not always result in a correct fuel level in the bowl.  Have you checked the fuel level in the bowls via the clear tube method?

I have not, I don't know what that method is

This is kind of hard to explain.  I think it might be covered in the clymer manual for cb750.  you need some clear tubing and some sort of fitting you can put in your float bowl drain screw hole.  First remove float bowl drain screw and drain float bowls.  Screw fitting into drain.  I use a tapered plastic vacuum nipple and just press in and twist to sort of let the drain's threads self tap the plastic.  Some have just heated the tubing and stuffed it into the drain.  It seals good enough.  Connect about a 6"-8" piece of clear tubing to the nipple and hold it up along side the float bowl.  Turn on the petcock.  Watch fuel level rise in the tube.  It will stop exactly where the fuel level is in the bowl.  Shoot for 3mm below the gasket and all 4 carbs at the same level.  All four carbs can be checked on the bike in this manner.  Just hold the tube for the inside carbs against the bowl of the outside carbs and as long as the bike is level side to side, the reading will be the same.


above pics are from a cb350k3 but the idea is the same...top pic is a decent level, bottom pic is bad and that cylinder would not even run.  Both pics the float height had been measured and set the same.

[cheftuskey121]

Something to note. My carbs are level with the ground, not at a slant with the engine. I've seen lots of pictures and all the carbs are slanted with the engine. My air box is not straight due to the carbs being straight. Can't have it both ways as the air box boots are slanted. I've done lots of poking around reading. This can't be helping the issue at all. I read hondaman post to someone about correcting that and getting the carbs slanted.  Bought some new boot clamps so as soon as they arrive ill be correcting the carb orientation along with checking everything else. Love the idea of the clear tube method. I will check that first. I know those levels are low.

[Henning]

Something is way out of kilter here. On my K1 I have three HM341's and one HM300 (a mess, I know). To fight the rich running I went from 120 to 115 on the mains, moved the needle clip from the middle to second from top, and when that wasn't enough, started backing out the idle air screws 1/8 of a turn at a time. I ended up at 1 3/8 turns out, except for the carb with the HM300, which is at 1 1/8. It's not quite there yet, but it cleared up a slight flat spot off idle, I get better mileage, and it cleared up the cream problem in the oil tank because it's running hotter.

So, is your timing correct, advancer working properly, camshaft aligned correctly etc. etc.? Also, there's currently a thread about ethanol in the petrol (gas) making the plugs burn white, but not because you're running lean, so you can't rely on that to check your mixtures anymore.

[iron_worker]

Having your carbs angled differently than factory can and will affect your mixture. It effectively alters what fuel level you need so the jets are immersed to the same depth as they would be factory.

Do you have the correct head/carb boots? Are they mounted correctly? My carb boots have a either a 1 and a 4 on them or a 2 and 3. When mounted correctly, the 1 faces up on the #1 cylinder, the 4 faces up for the boot on the #4 cyclinder ...etc etc

Having the boots mixed around between cylinders or rotated incorrectly could conceivable change the angle of the carbs I think.

IW

[cheftuskey121]

Something is way out of kilter here. On my K1 I have three HM341's and one HM300 (a mess, I know). To fight the rich running I went from 120 to 115 on the mains, moved the needle clip from the middle to second from top, and when that wasn't enough, started backing out the idle air screws 1/8 of a turn at a time. I ended up at 1 3/8 turns out, except for the carb with the HM300, which is at 1 1/8. It's not quite there yet, but it cleared up a slight flat spot off idle, I get better mileage, and it cleared up the cream problem in the oil tank because it's running hotter.

So, is your timing correct, advancer working properly, camshaft aligned correctly etc. etc.? Also, there's currently a thread about ethanol in the petrol (gas) making the plugs burn white, but not because you're running lean, so you can't rely on that to check your mixtures anymore.

my timing appears to be correct yes. it is slightly off the advance mark, and because this is my first bike, I don't really know what I am looking for. I havent see any videos and I dont have anyone local to help me out. I can only learn so much from reading. I don't know what a healthy advancer is supposed to be like, but at about 2500 rpms the strobe light shows the timing advanced as much as possible, even if its not completely reaching the advance // marks.

I have been using non ethanol gas here. fortunate to be on the water so there is plenty of ethanol free gas for all the boats! I can tell that the engine is too hot. I know for a fact right now I am fuel starved, those fuel levels in the bowls are just too low.

IW it makes perfect sense, the slow jets are barely dipping into the level causing the starvation, lack of fuel combustion just off idle. I will get those carbs tilted back. also about to go through the carbs again. I DO have cb750 specific boots, and they are labeled and I have them on the right ports. in order to get the carbs "flat" I had to twist the boots slightly, I will get them straightened out upon reinstallation.

hopefully I can report back better things soon. thanks for all the insight guys.

[cheftuskey121]

rotated incorrectly could conceivable change the angle of the carbs I think.

IW

the funny thing is I DID that on purpose because I thought the carbs should be level with the ground. whoops.

[cheftuskey121]

alright, tried the clear tube method and it worked wonders for showing me my fuel level......unfortunately (or fortunately) my fuel levels are all the same, about 1/4 inch from the gasket area. carbs are still coming off.

sidebar. my oil smells like gas. fairly strong. enough to remind me of my dads KX250, a 2 stroke motocross bike. also my exhaust smells a decent amount of gas. is it possible I am getting sufficient fuel through the carbs, but there is constant blowby of fuel past the pistons getting into the oil and exhaust...causing the lean condition all the time? I think this makes sense in theory. seems like an engine teardown and rebuild, something I am not ready for right now. if this engine has to come apart it I am just going to rebuild a donor motor, granted that I find one. sigh. carbs still coming off, checking everything, orienting boots properly, etc.

if my theory is correct then can I raise the needle jet one notch and prolong my engines inevitable doom so I can ride the damn thing until I can get another motor etc?

I should add I do not get smoke from the pipes of any kind, and no bluing of the pipes....so it LOOKS like things are fine from the outside. it also SOUNDS like things are fine. i have no other motorcycle let alone another cb750 to judge on smell, but it smells like 2 stroke gas/oil.

[cheftuskey121]

one more thing. just changed the oil again after only 700 miles. Rotella 15w-40 (the dino diesel oil). the oil was nearly black. very very dark, and smelled of gas.

[nevernoluck]

If you really think you have blowby, compression test is in order, you can buy a gauge or rent one from an auto parts store, but if you have that issue you should have wet black plugs

[Vinhead1957]

Chef didn't you have an overflow problem a couple weeks ago? That would account for the smelly oil

[cheftuskey121]

Chef didn't you have an overflow problem a couple weeks ago? That would account for the smelly oil

I think I did but I am pretty sure I changed the oil....maybe not. I need to write things down! too much riding and not enough paying attention. I mean can you blame me though. these bikes are the cat's pajamas!

early to bed, up early tomorrow for work. tomorrow I am going through the check up again to make sure my timing, cam chain, and valves are good, then carb sync. I have searched for "3000 mile tuneup" and cannot for the life of me find where someone actually lists the proper order. just a lot of "search for 300 mile tuneup". irony. I have scoured the honda manual too and find all of the procedures, but not an order. last time I did it I did cam chain, valves, timing. is this right?

[bender01]

You had the Bike on I-95 for 25? miles.. Did it pull 80 plus (steady not WOT) no problem? If so seems the floats would be pretty close.

[cheftuskey121]

You had the Bike on I-95 for 25? miles.. Did it pull 80 plus (steady not WOT) no problem? If so seems the floats would be pretty close.

yeah Ben I had it on 95 for 50 miles doing 70-85. holding steady cruising with no issues.

[scottly]

alright, tried the clear tube method and it worked wonders for showing me my fuel level......unfortunately (or fortunately) my fuel levels are all the same, about 1/4 inch from the gasket area. carbs are still coming off.

1/4 inch is on the lean side of fuel level. Make sure you shut off the petcock when the bike isn't running, as float needles can weep fuel when sitting and foul the oil, but not show up if the demand for fuel exceeds the weep.

[cheftuskey121]

alright, tried the clear tube method and it worked wonders for showing me my fuel level......unfortunately (or fortunately) my fuel levels are all the same, about 1/4 inch from the gasket area. carbs are still coming off.

1/4 inch is on the lean side of fuel level. Make sure you shut off the petcock when the bike isn't running, as float needles can weep fuel when sitting and foul the oil, but not show up if the demand for fuel exceeds the weep.

Understood. Makes sense. The fuel gets shut off regularly, I've never left it on. That's another thing that's odd to me