Bogging down

[taz]

1972 Wombat ! when out scooting around the desert and I crack the throttle it seems to bog down a bit then takes off ... Any suggestions would be nice , than you ...

[Zyx]

The possibilities are many. Jetting comes to mind first. But also possible: clogged exhaust; compression leak; worn rings and piston; timing; clogged pilot passages and jet; old gasoline; worn needle jet and/or needle.

How long have you had it? Has it always been this way or is it something new? Have you recently moved to higher elevation? How many hours/miles/years since the top end was overhauled? The more information provided, the easier the diagnosis.

[taz]

Ouch on me ! Just had a bore and new piston and just melted it ! Not a happy camper right now !!! Maybe time to sell .........

The possibilities are many. Jetting comes to mind first. But also possible: clogged exhaust; compression leak; worn rings and piston; timing; clogged pilot passages and jet; old gasoline; worn needle jet and/or needle.

How long have you had it? Has it always been this way or is it something new? Have you recently moved to higher elevation? How many hours/miles/years since the top end was overhauled? The more information provided, the easier the diagnosis.

[hodakamax]

Taz, I hate to lock the gate after the horse is stolen but this story plays out somewhat often on a two stroke engine without a fuel filter. Since two strokes get all their lubrication through their jets,(at least on your model), clogged jets can not only cause lack of lubrication but a lean condition which leads to overheating, surpassing the limits of the lubricants. Of course all of the things that AZ mentioned (timing,old gas etc) can lead to these problems also. Several other factors can come into play such as insufficient clearances or lack of break in, but a clogged jet,or at least jetting, as he mentioned, comes to mind in this situation. Hard to tell what the culprit is without an investigation of the carb and piston assembly. It's hard to sell a bike with a seized engine, probably a good idea to analyze the situation and go from there. Most of us have been there, don't give up!

Max

PS-- the Gang is here to help!

[Bullfrog]

I'm sorry we are all too late in responding. Answers to Arizona's questions would help diagnose what the problem was.

Ed
PS: My "knee jerk" reaction was that your jetting was lean somewhere in the middle range of throttle position (but that is really just a WAG - Wild A _ _ Guess) And that is only ONE possibility in a range of MANY possibilities.
PPS: Which leads to the sorts of questions Arizona raised. Why would it be lean? Did something change? etc. etc. etc.

[michael_perrett]

Leaking crankshaft seal and/or an air leak at a gasket

[taz]

OK , Fresh fuel & oil 30 to 1 mix , clean carb & adjusted , new fuel filter , new piston & ring ( wiseco ) & top end gaskets , exhaust clean , points open right at mark ! ... Start up was nice with nice blue smoke adjusted idle and then for a little putt all good . Next day same and while ridding with changing revs up and down for a little break in it stumbled and I never gave a thought and just bump started it ran good a little bit more then wham stalled motor . Pushed home let cool down and no compression , tore into it to find ring melted into piston at the front ( exhaust side ) My findings so far was I noticed in carb the c clip on the needle was one notch above middle ( maybe ? ) Other than that I'm stumped ! Before I rebuild the bottom end any other suggestions on what I have listed here ? Thanks to all ...................

[Dale]

Like Michael stated, it sure sounds like an air leak. An air leakdown test is always recommended on a rebuild. It is still possible that it was just a lean condition, but for it to melt so fast, I would suspect an air leak.

[hodakamax]

When melting occurs, it got too hot. Too hot is caused by friction ( which includes lack of lubrication) between parts or lean conditions. Break-in is a critical time in an engines life because clearances are at their minimum. All this said, It can be difficult to resolve what caused a melting event. As Bill Chapman says,"Being too lean 'for the conditions' are the cause of most seizures" and that's my theory also. I personally break in an engine ridiculously rich and slowly back off from there.

Excessive jetting however can't cure too tight of clearance problems such as too small of ring gap or piston clearance. Sometimes engines work perfectly in certain conditions but add several other factors at once, such as new tighter clearances, an air leak, perhaps a different altitude etc. and the "conditions" have changed causing a too lean (again, for the conditions---heat is building to the point off lubrication failing) problem.

Of course all of Max's ramblings hasn't pinpointed a cause but I guess what I am saying is that conditions can add up to points of failure and that's why I always start with that ridiculously rich jetting when new conditions are present.

Just my humble opinion,

Max

[taz]

When melting occurs, it got too hot. Too hot is caused by friction ( which includes lack of lubrication) between parts or lean conditions. Break-in is a critical time in an engines life because clearances are at their minimum. All this said, It can be difficult to resolve what caused a melting event. As Bill Chapman says,"Being too lean 'for the conditions' are the cause of most seizures" and that's my theory also. I personally break in an engine ridiculously rich and slowly back off from there.

Excessive jetting however can't cure too tight of clearance problems such as too small of ring gap or piston clearance. Sometimes engines work perfectly in certain conditions but add several other factors at once, such as new tighter clearances, an air leak, perhaps a different altitude etc. and the "conditions" have changed causing a too lean (again, for the conditions---heat is building to the point off lubrication failing) problem.

Of course all of Max's ramblings hasn't pinpointed a cause but I guess what I am saying is that conditions can add up to points of failure and that's why I always start with that ridiculously rich jetting when new conditions are present.

Just my humble opinion,

Max

When you say rich , what would you suggest I do to all components to start ??? Thank you

[hodakamax]

Taz, when I speak of rich during break-in I'm speaking of the main jet. The last rebuild with new expensive piston and new bore that I did , I increased the main jet by several numbers and tested the engine. It would smoke and four stroke and I proceeded downward on the main where it was still too rich but drivable. It still could be driven at mid throttle but with a lot of smoke. I rode about 30 minutes at varying speeds. Another two changes on the main and about another hour of time the engine ran only slightly rich at full throttle and a new plug was showing rich conditions. Down one more on the main and the new plug was showing slightly rich and still smoking exhaust. A new plug and off to a three hour race, I figured a fouled plug during the race was easier to fix than a rebuilding the engine. The plug was black after the race and the engine was flawless.

I don't know if I'm answering your question but the failure could have been caused by the new tight engine being too lean "for the conditions". It's just detective work from here, checking all the components, even the carb (again) for a clogged jet or passageway. In my early days as a Hodaka dealer engine seal failure was almost non-existant but with 40-50 year old engines common. As the guys are mentioning I certainly would replace the seals. Air leaks cause lean conditions. The bore will probably clean up but it sounds bad for the piston. Too tight of clearances and ring gap can be culprits and even though you checked the timing once doesn't mean something hasn't changed. Don't forget the easy/rich break-in.

I know you're frustrated at this and I seem to still be rambling today, but If you can post some pictures of the damage the Gang will certainly help.

Maxie

[taz]

Ramble all you want it all makes sense ! Here is the piston , ran the hone about 4 to 6 times up and down and it cleaned right up ... Oh and its manly on the exhaust side ...

[Zyx]

That was a pretty hard seizure. The picture gets a bit fuzzy when expanded but looks like some of the ring is missing in the area of metal transfer. Since this was a new piston and ring, I have to ask - who set up the ring clearance? Was it built by someone else for you, or did you install the piston and ring?

The reason I ask is this: new piston and ring are rarely if ever ready to install as they come out of the package. The ring is most always too long, intentionally. You have to set the ring end gap to suit the installation, which Wiseco can not control. Nor can any other manufacturer, which is why the ring is made a bit long. The end gap needs to be filed to spec to fit your cylinder.

The ring in your case appears to have jammed up tight end to end, and may have even forced some of the ring to expand into the exhaust port, either distorting the piston ring land or shearing off some of the ring. In either case, failure would be moments away.

Another often overlooked aspect of a new piston is the wrist pin. Rarely is the out of the box pin clearance correct for the wrist pin, and here I can only guess why. My guess is tolerance control. Pistons are made, in this case, by Wiseco, but the wrist pin is made by a different machine shop. Pins may be held to a stated tolerance, as would be the pin bore in the piston, but the combination of tolerance as between pin and bore can't be strictly controlled, so the bore is generally a bit small, and pin fit will be really tight. The pin bore needs to be lapped until it fits the pin with a push fit. It shouldn't fall through the hole, but it should not take tools to push the pin into place. Too tight a pin will grossly shorten piston and rod life, but would not cause the seizure you had. Only mentioning it because it is part of piston fitment.

Closely inspect the upper edge of the exhaust port and see if there is any collision marking there. If there are burrs, dress them out and be sure there is a bevel on the upper and lower edges of the exhaust port, as well as all the other ports.

If you didn't set up the ring on installation, ask the one who did what gap it was set to. If you did it, what gap did you use? You may want to open the gap to the high side of recommneded gap. Better to have a bit too much than not enough gap on the ring.

Practice varies between techs, but I don't rejet for breakin. I have been known to use a richer oil mix for the first tank, but only a little. Too much oil just makes it run hot, and overly rich engines can also run hot, so I don't rejet. Varying engine speeds are okay mostly because it is hard to run a bike without varying engine speed. Long sustained full throttle is of course not recommended for fresh engines. I would say just ride normally, but not for long periods. Get the engine fully warm by riding around running through the gears and not pushing hard, and then park it and let it cool fully. Repeat. Repeat again. Each time ride a bit farther between cycles but let it cool down between runs. After a half dozen runs or so, it is about as good as it is going to get. Unless you have a nitride bore, two strokes break in pretty fast. Just stay away from peak rpm pulls until it has some hours on the clock.

[taz]

Bore had 3000 clearance and I set ring gap at .009 ports had no edges ... So far I have found in carb that the ring on the needle was one mark leaner than the middle and the main jet is a 150 , I'm still tearing into things ...

[hodakamax]

All good info from AZ on ring end gap and break-in. When R pistons for Ace 100s were $8.00 and $2.75 for a ring,(plus $8.00 for a rebore) break-in didn't seem as important as it is today with $150+ pistons, maybe that's why I'm overly cautious on my personal rich break-ins.

Of course a new piston/ring looks to be needed. I have salvaged a piston like that but it usually is not too successful. It's hard to get the ring out without breaking it. If you do succeed you can measure the end gap in the cylinder. Repairing damage to the ring groove is tough (but can be done with small files and such) to restore the clearance needed for the ring to move freely and perhaps worth a try, what have you got to lose? If all that works sand the high points off the piston and check clearances. Might work--maybe.

Maxie

PS-- a little more thinking on leaking seals, maybe the engine with its new found compression did indeed pull more air from the worn seals creating or adding to the lean condition and causing more heat. Detective work is always thought provoking!

[Zyx]

Taz,

When you say the ports have no edges, what are you referring to? I was suggesting inspection of the port edges closest to the piston, i.e., looking at the ports from the top of the cylinder bore. The ports should have a chamfered edge of something like one to two mm. A port edge that is square to the bore will snag rings. Any ring will expand slightly into the port as the piston moves up and down. The chamfer is to ease the ring back into position as the ring approaches and passes the port edge. So, if you mean the edges are square without chamfer, that's bad and will almost guarantee your rings won't last.

If I have misunderstood what you mean, I apologize and could you explain again.

[hodakamax]

I should probably clarify some of my statements on a rich break-in. Normally after a rebuild an engine, I increase the main jet by one or two steps and break the engine by running the engine at differnt speeds and avoiding high RPMs and getting the engine too hot. Heating and cooling cycles also promote a good break-in.

On my post above on extreme rich jetting was when the engine was rebuilt and the 24mm carb was replaced with a modern new spigot 28mm. The new 28mm was an unknown to me so I proceeded with extreme caution by starting with a large main and working my way down (way down).

Changing main jets is an easy task and one or two jet sizes helps to protect (more oil and more fuel) during the critical first minutes of a new engine break-in. The new engine also has a lot more compression than it probably had before which could possibly effect the jetting. I always try to err on the rich side, not the lean.

Max's opinion,

Maxie

[Zyx]

Erring on the rich side is proper procedure.

[taz]

OK going all out , ordered bottom end rebuild kit and new top end rebuild kit . also ordered three main jets 200 , 190 , 180 with a 35 pilot jet , now for tear down .................

[hodakamax]

Cool Taz! We don't want you to sell out. Here's a diagram of the port chamfering that AZ was talking about from an old bulletin about flat track modifications. As AZ says, very important. Keep us posted on the project!

Max

[taz]

Cool Taz! We don't want you to sell out. Here's a diagram of the port chamfering that AZ was talking about from an old bulletin about flat track modifications. As AZ says, very important. Keep us posted on the project!

Max

NICE !

[taber hodaka]

Taz in your first post you stated when you opened the throttle the engine bogged, or was it a flat spot a delay. If it were a flat spot or a momentary delay that is the sign that you are lean on the mid range. If that is the case then increasing the main jet is not going to help. I start with larger main jets and tune the mid range and lastly determine the main jet I need for proper tuning. ++++++ Clarence

[taz]

Taz in your first post you stated when you opened the throttle the engine bogged, or was it a flat spot a delay. If it were a flat spot or a momentary delay that is the sign that you are lean on the mid range. If that is the case then increasing the main jet is not going to help. I start with larger main jets and tune the mid range and lastly determine the main jet I need for proper tuning. ++++++ Clarence

Yes you described it perfectly ! How do I enrich the mid range Thanks ....

[hodakamax]

Hey Taz, on the Strictly Hodaka site under FAQ, there's a brief guide to Mikuni tuning. You will see that most of the mid-range is controlled by the position of the needle jet by the position of a clip on grooves on the needle. A higher groove selection lowers the needle into the jet,(leaner) and lower grooves are richer (raising the needle from the jet--richer.) However a main jet change also effects the needle setting. A larger main jet also makes the mid range more rich but only about 10%.

When you increase the main during break in you are also making it slightly richer mid range. Most seizures occur at full throttle and usually at high RPM. I'm starting think more and more that the seizure was caused by air leak making it too lean everywhere. No amount of jet and needle tuning was going to cure a ever increasing lean condition.

At least that's my thoughts for the day.

Max

PS--Also you stated that when you "opened the throttle" the bog occurred. Full throttle is controlled almost entirely by the main even though you were at mid RPMs--something to think about anyway. (Complicated huh!)

[taz]

Hey Taz, on the Strictly Hodaka site under FAQ, there's a brief guide to Mikuni tuning. You will see that most of the mid-range is controlled by the position of the needle jet by the position of a clip on grooves on the needle. A higher groove selection lowers the needle into the jet,(leaner) and lower grooves are richer (raising the needle from the jet--richer.) However a main jet change also effects the needle setting. A larger main jet also makes the mid range more rich but only about 10%.

When you increase the main during break in you are also making it slightly richer mid range. Most seizures occur at full throttle and usually at high RPM. I'm starting think more and more that the seizure was caused by air leak making it too lean everywhere. No amount of jet and needle tuning was going to cure a ever increasing lean condition.

At least that's my thoughts for the day.

Max

Another great write ! Thanks , I'm sure after all I have read on here that after my rebuild and cautions things are going to look a lot like Christmas ... Than you every one for the fantastic support !!!