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Post by motodude on Aug 3, 2023 11:46:22 GMT -5
Hey everyone! I know, another bbk issue. So prior to installing a 50mm bbk there was a very slight tap every now and then. After the bbk it taps at idle and on acceleration. But on deceleration it’s perfectly quiet. It’s not the valves as I’ve set them to .003 and .004 and listened with the valve cover off. Perfectly quiet. I’m just stumped. I’ve listened around the engine multiple times and it SEEMS like it’s around mid engine area. Very hard to pinpoint though. Any help is GREATLY appreciated. Thanks.
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Post by FrankenMech on Aug 3, 2023 17:22:15 GMT -5
Preignition due to low octane fuel, lean mixture, or high compression? There can also be other reasons like a hot spot, improper spark plug or loose spark plug etc.
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Post by GrumpyUnk on Aug 4, 2023 9:20:01 GMT -5
What size BBK? Original cylinder head? Bigger jets or stock? What octane fuel is used?
tom
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Post by motodude on Aug 5, 2023 13:49:27 GMT -5
Preignition due to low octane fuel, lean mixture, or high compression? There can also be other reasons like a hot spot, improper spark plug or loose spark plug etc. I’m not actually positive what octane fuel I had in the can. I will fill it with 93 next time and see if that does anything. I jetted the main to a 98 and removed some restriction from the exhaust. Still runs a tad rich. Spark plug is correct and nice and tight. I’ll have to check compression once I get a tester. It’d be nice to have one anyway! |
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Post by motodude on Aug 5, 2023 13:51:49 GMT -5
What size BBK? Original cylinder head? Bigger jets or stock? What octane fuel is used? tom it’s the 50mm bbk. It’s all stock, I just bought the cylinder kit with the piston and gaskets etc. 98 main jet and and a bit rich. thanks for the help guys!! |
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Post by GrumpyUnk on Aug 6, 2023 10:48:28 GMT -5
The 50mm is at the very thin margin of having a too high compression ratio which can lead to ping and pre-ignition. You are compressing a larger volume 49cc vs 8xcc.(memory), which raises he CR significantly.
I don't know if you will get by with it or not.
I also remember getting a main jet that was larger when I went to 72cc. I think it was a 105, but don't bet the farm.
tom
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Post by motodude on Aug 7, 2023 19:36:58 GMT -5
The 50mm is at the very thin margin of having a too high compression ratio which can lead to ping and pre-ignition. You are compressing a larger volume 49cc vs 8xcc.(memory), which raises he CR significantly. I don't know if you will get by with it or not. I also remember getting a main jet that was larger when I went to 72cc. I think it was a 105, but don't bet the farm. tom I gotcha. That makes sense. That’s what I’m worried about, but I may just send it with 93 octane and if it ever goes, I’ll just rebuild everything. Kinda wanted to anyway for peace of mind. Thanks a ton for the assistance! |
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Post by FrankenMech on Aug 8, 2023 8:34:22 GMT -5
AFAIK most scoots require premium fuel, octane numbers vary with your local altitude. The fuel system materials usually require 100% gasoline, no alcohol.
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Post by GrumpyUnk on Aug 8, 2023 12:21:59 GMT -5
Frank, most recommend based on a different rating system, which equates to 87. The 87 is (R+M)/2, I think. Research method and Motor method are the two procedures used in US to determine fuel octane. It's posted on the pumps. Anyway, the China specified is right at 87 when converted to the US posted. FWIW.
If one increases the CR by installing a BBK, then it may be higher octane fuel is required to prevent ping/pre-ignition. I would not be surprised a bit. I did try some non-ETOH 90 octane in a 72cc BBK and noted no difference at all. Again, FWIW.
As far as ETOH added to the fuel, it raises octane rating, and by now the China machines should be able to handle it without deteriorating too much. I have not noted any bits getting ruined by our adulterated fuels. Could be missing something, but I have seen nothing of note.
YMMV ... and will.
tom
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Post by FrankenMech on Aug 8, 2023 21:57:19 GMT -5
Tom, the (R+M)/2 method has been used since the late 60's here in the US. Most equipment manuals for foreign equipment I have seen still use the RON number which is research octane number. The RON number was generally higher than the motor number hence the confusion at the pump. The old Motor method was used in some regions and companies in the US and was replaced by the (R+M)/2 method as noted above to solve(increase LOL) consumer confusion. Without a Motor number for the fuel or equipment in question it is hard to average the RON with an unknown number to determine the required octane number.
The addition of ethanol does increase the octane number but it also decreases the available energy per gallon. Alcohol for fuel is heavily subsidized by our taxes for political reasons.
I still see a number of people on here having the same old problems with water, corrosion, and fuel/vac line deterioration caused by alcohol. The new EFI scoots may be better. Alcohol in fuel is a US 'legislature generated problem' to appease agricultural interests during the old oil embargo days and is not mandated in China or most other countries, only the US government was stupid enough to do it.
Alcohol is also used in some foreign countries as a substitute for petrochemical derived gasoline. To use alcohol efficiently requires much higher compression engines.
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Post by GrumpyUnk on Aug 9, 2023 11:13:39 GMT -5
I went somewhere on the web to determine what rating is used in China. I do not remember what it was, but there was a formula to convert from that rating to the average used in USA. Their 90 fuel was equivalent to 87 rating posted on the dispensing pumps in the US.
I wanted to know if US average 90 was required, and it is not.
ETOH adds octane but removes BTU, having a 15-16% penalty(likely not exact). It won't ping as readily but you won't go as far on a gallon.
The US has had ETOH mixed with gasoline for some time. I think longer than the sale date/production date of the high majority of 139QMB scooters roaring about the countryside. IOW, they all SHOULD handle ETOH in the fuel w/o damage. Recent readings indicate that the alcohol doesn't seem to cause as much damage as some have claimed. But. BUT. My take is if you leave it in the float bowl for a while, inexact while, it will degrade into a goo and cause rust if the bowl is made of Fe. Wait longer, and it will start to cause corrosion on the Al-mix used to make the carb body, jet holder, etc.
IOW, not a 'good thing' for carbs. I think that applies to all small engine carbs. Including outboard motors and chain saws.
I will use it, but try to keep the liquid in the bowl, if left stored, fresh or drained completely.
I have a Honda CB350 since new that somehow got the fuel tank corroded. It never had alcohol-laced fuel, but was stored in an unconditioned garage. The inner surface got rusty and slightly pitted. I cannot blame ETOH.
I used some 'cleaner' and some coating and it seems OK, but I have read that ETOH may make the coating come free of the metal.... and make a huge bleeping mess inside a somewhat inaccessible area. yay team. not.
tom
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Post by FrankenMech on Aug 9, 2023 17:26:32 GMT -5
"Should" You are assuming that china manufacturers and part suppliers are interested in complying with US fuel standards, -I don't think so... They make scoots and parts by the thousands at the lowest cost and don't care where they are delivered and used. The water that alcohol attracts is corrosive to steel, aluminum, zinc, and brass. When those materials are mixed in an assembly and electrons are free to travel between the metals dissimilar metal corrosion will occur. Ethanol/gasoline mixes are not well tolerated by elastomers (rubber) materials well. Some elastomers will tolerate a 10% ethanol mix at room temperature but the environment around an engine is hotter than that. Elastomers that will tolerate those 10/90% mixes are extremely expensive and are not used in any great quantity. Think 'Viton' float needles. The ethanol causes the elastomers to swell and crack in a characteristic pattern that can be seen with magnification. A few will tolerate a 5/95% mix at somewhat higher temps but the Gov't reps heard 10% and ignored any information to the contrary while they filled their pockets with bribes -er- campaign contributions, expensive gifts, low interest loans, -which were frequently forgiven as long as they voted certain ways, etc... It has come to light that even members of the supreme court have been bought by special interests and they don't even have to campaign for re-election... Protective coatings can be used but they are not a simple 'pour and coat' solution for the corrosive effects of water and dissimilar metal corrosion. Special surface prep is required so it is not used on least cost applications.
The fuel we buy at the pump can not be trusted to have no ethanol in it because the financial incentive to cheat on the alcohol content is too great. You can also not depend on the alcohol content of 10% fuel not being higher than 10% for the same financial reasons.
Closed containers of fuel will breathe due to temperature changes and draw in moisture laden air. Metal containers are best while those polyethylene gas cans will soak up moisture even through the material itself called permeability. Those small water molecules get through most plastics. Alcohol molecules will attract water.
Sorry, I must stop typing now, my hands are too sore.
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Post by GrumpyUnk on Aug 10, 2023 11:30:42 GMT -5
As a teen, I ran a gas station from 6 'til midnight. Alone. What a fool. It was on a 2-lane highway that led right out of town. Fearless and ignorant, but that would be around 55 years ago.
I remember well the smell of Sunoco fuels. And all the rest. What is sold today is totally different. Given that Pols have their fingers in the pie/recipe/?? there's not a lot one can do.
Adding some H2O to ETOH E-10 should cause the alcohol to precipitate out of solution(suspension?) so the top layer is gasoline without any ETOH. I expect the octane to be lower, but the BUT/l higher. For most outdoor equipment, such as mowers, graders, tillers, etc, the lower octane is fine, and there would be less opportunity for H2O to get into the equipment and cause damage. It can be done at home with a big enough jug and the ability to pour off the non-ETOH fuel without transferring H2O. Worth it? Depends. The remains would likely store better than the E-10, and maybe reduce the damage incidence.
I figure I should just use the equipment and keep the fuel fresh, or drain the float bowls(tanks?) and use what they sell.
I do not ride enough that I ever fill the tank, and certainly can drain the tank via the float bowl drain(done multiple times) so I don't have corrosion problems when stored.
So so so much fun brought to us by the clown show along the Po-To-Mac. May they all lose re-election and have to find a real job. Sure. That's gonna happen... not
tom
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Post by FrankenMech on Aug 10, 2023 16:39:17 GMT -5
Using metal gas cans I can often see those big pools of water in the bottom of the can. Decanting does work as you say but the remaining volume of fuel is less. As a teen there were a pair of serial murderers roaming across the country. I was the only gas station attendant left alive after they visited a station. I do not know if they ever caught them. I just moved very fast that night and disturbed their routine. Being interrogated by the FBI, KBI, Police Chief, Sheriff, AG, and the DA kept me out of class one afternoon, but sure raised a few office staff eyebrows around the high school. They did a good job of hiding the fact I was in the conference room with them. I wasn't able to give them more than a general description and the make and model of the car. There were lots of rumors around school. I was about the same age, situation, and temperament as you were. At night I often stayed late and kept the station open as long as cars were running over that bell, sometimes almost to midnight or 1PM. Sales were $1,2,or$3 each but gas was $0.25/28 per gallon. We usually closed at 9PM. Some of those nights I sold as much gas as we did all day long. Most nights I had friends for company at the station. The night I avoided getting a bullet in the brain was a normal 9PM closing night. Once those Po-To-Mac denizens get into office to feed at the public trough it is very very hard to remove them.
To the OP, Sorry about a couple of old farts reminiscing. I have heard of many users adding a second or thicker base gasket to the cylinder to reduce compression, or a thicker head gasket.
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