Search Members Calendar FAQ Portal
Welcome Guest [Log In] [Register]
  • Navigation
  • Fizzytalk
  • →
  • Fizzy Chat
  • →
  • Fizzy Problem Solving
  • →
  • carb settings
Add Reply
carb settings
Tweet Topic Started: Aug 10 2016, 09:38 PM (125 Views)
bolder Aug 10 2016, 09:38 PM Post #1
The 65mph Club Member
[ *  *  *  *  * ]
Posts:
149
Group:
Members
Member
#6,413
Joined:
May 13, 2012
Hi,

I have two bikes both 394 type. fitted with parma kits and cut disc.

The one is running fine has 170 main jet. needle valve one notch down from middle and air screw out 2.5 turns out.
The bike starts easy and goes well.

The problem bike has a 170 main jet.

When the air screw is 2.5 turns out the bike is a pig to start,so I reset it at its highest revs on tick over which was 2 turns out and then reset it for best throttle response which is 1.5 turns out .
The bike starts alot better .
When the needle valve is set in the middle groove the bike goes well but the engine makes alot of noise like piston slap, pinking sound or metal to metal sound not good.
When the needle valve is set in the one groove down from mid. (richer) the bike smokes and bogs down mid. range but the engine sounds alot better.
Then I adjusted the mixture screw to 2 then 2.5 turns out to make it weaker still bogs down and don't like starting.

Tried a 165 jet in carb. and done all of the above but the engine was very noisy.

I've change plug from a 7 to a 9 no change.

Both bikes run on supper unleaded.

What would you say to look at next timing.

Thank for looking


Edited by bolder, Aug 10 2016, 10:08 PM.
Offline Profile Quote Post Goto Top
 
mech73 Aug 11 2016, 07:00 AM Post #2
Member Avatar
Fizzmeister Extrodinaire
[ *  *  *  *  *  * ]
Posts:
3,067
Group:
Members
Member
#2,607
Joined:
May 19, 2007
Definitely set timing before adjusting carb.

Engine noise changing with minor carb settings is unusual, could the noise changes be as the engine is warming up?

It is possible for a an over rich mixture to reduce pre-ignition, but the underlying reason is usually over high compression ratio or over advanced ignition timing.
Offline Profile Quote Post Goto Top
 
bolder Aug 11 2016, 08:07 PM Post #3
The 65mph Club Member
[ *  *  *  *  * ]
Posts:
149
Group:
Members
Member
#6,413
Joined:
May 13, 2012
Hi Mark,
Thanks for the info.
I've checked the timing with a D.T.I and found it to be 1.3 b.t.d.c so I adjusted it to 1.4.

Adjusted the needle AGAIN back to mid. position air screw still 1.5 turns out .

Bike starts first kick but bogs a little in mid. range.

I'm running 33-1 with semi synthetic which a lot of people don't agree with but this is the instructions I got with the kit from Darrell Taylor.
I own a boat no not Sunseeker lol and the mix for the engine in that is 100-1?

When I have time I will check the piston for slop and change the small end for a genuine one,It should be ok as its only done 3k miles.

It's mot day tomorrow so I will ask the guy to have a listen to the engine and see what he thinks as he's been working on bikes all his life

I will let you know how I get on
THANKS for your time



Offline Profile Quote Post Goto Top
 
mech73 Aug 11 2016, 10:12 PM Post #4
Member Avatar
Fizzmeister Extrodinaire
[ *  *  *  *  *  * ]
Posts:
3,067
Group:
Members
Member
#2,607
Joined:
May 19, 2007
Standard timing is 1.8mm BTDC, so at 1.3mm or 1.4mm you definitely don't have over advanced ignition. That setting may lose a bit of mid range power, but is unlikely to be the cause of any engine noise.

A weak oil mix is also unlikely on it's own to cause a noise straight away, although over time it might due to increased wear. You've set me off now :P I have to say, I've never understood the reason for using less oil than Yamaha recommended. I know boat engines run very cold and generally don't rev quite so high, so the oil condenses out more rapidly in the crankcase, and on the water plug fouling can be inconvenient. Fizzies are at the other end of the spectrum with an air cooled iron cylinder. The way we use them also means they can be at full revs sometimes for miles without a break. Under these conditions very little oil condenses out, so you need more in the mix to compensate. It's 20:1 all the way for me for reliable thrashing.

I don't think oil mix is the cause of your noise issue though, nor timing. And I find it hard to think it can be small carb changes. It's more likely something mechanical. Possibly just piston slap or the rings catching on the exhaust port. A big chamfer on the port edges can help, especially the lower edge of the exhaust port. It could still also be an over high compression ratio. You could compare the head volume with the one that runs better and quieter.
Offline Profile Quote Post Goto Top
 
Jasper Carrots Funky Moped Aug 12 2016, 05:37 AM Post #5
Member Avatar
Plods on at 30
[ *  *  *  *  *  * ]
Posts:
752
Group:
Members
Member
#5,397
Joined:
June 13, 2010
bolder
Aug 10 2016, 09:38 PM
Hi,

I have two bikes both 394 type. fitted with par ma kits and cut disco.

The one is running fine has 170 main jet. needle valve one notch down from middle and air screw out 2.5 turns out.
The bike starts easy and goes well.

The problem bike has a 170 main jet.

When the air screw is 2.5 turns out the bike is a pig to start,so I reset it at its highest revs on tick over which was 2 turns out and then reset it for best throttle response which is 1.5 turns out .
The bike starts alot better .
When the needle valve is set in the middle groove the bike goes well but the engine makes alot of noise like piston slap, pinking sound or metal to metal sound not good.
When the needle valve is set in the one groove down from mid. (richer) the bike smokes and bogs down mid. range but the engine sounds alot better.
Then I adjusted the mixture screw to 2 then 2.5 turns out to make it weaker still bogs down and don't like starting.

Tried a 165 jet in carb. and done all of the above but the engine was very noisy.

I've change plug from a 7 to a 9 no change.

Both bikes run on supper unleaded.

What would you say to look at next timing.

Thank for looking


Your problem engine sounds exactly the same as mine, or should I say did, as at this very moment it is off the bike and in a garage hopefully getting unseized :X
Offline Profile Quote Post Goto Top
 
bolder Aug 12 2016, 06:30 PM Post #6
The 65mph Club Member
[ *  *  *  *  * ]
Posts:
149
Group:
Members
Member
#6,413
Joined:
May 13, 2012
mech73
Aug 11 2016, 10:12 PM
Standard timing is 1.8mm BTDC, so at 1.3mm or 1.4mm you definitely don't have over advanced ignition. That setting may lose a bit of mid range power, but is unlikely to be the cause of any engine noise.

A weak oil mix is also unlikely on it's own to cause a noise straight away, although over time it might due to increased wear. You've set me off now :P I have to say, I've never understood the reason for using less oil than Yamaha recommended. I know boat engines run very cold and generally don't rev quite so high, so the oil condenses out more rapidly in the crankcase, and on the water plug fouling can be inconvenient. Fizzies are at the other end of the spectrum with an air cooled iron cylinder. The way we use them also means they can be at full revs sometimes for miles without a break. Under these conditions very little oil condenses out, so you need more in the mix to compensate. It's 20:1 all the way for me for reliable thrashing.

I don't think oil mix is the cause of your noise issue though, nor timing. And I find it hard to think it can be small carb changes. It's more likely something mechanical. Possibly just piston slap or the rings catching on the exhaust port. A big chamfer on the port edges can help, especially the lower edge of the exhaust port. It could still also be an over high compression ratio. You could compare the head volume with the one that runs better and quieter.
Hi Mark,

I am only using 33-1 because that was on the instruction with the parma kits,Also set the timing to 1.4 BTDC ?

so if it is piston slap running it on 33-1 could be the cause?

When I use 20-1 mix will I have to change the carb setting?

Took the bike for mot and it started first time bog down for first mile then was ok.

The guy that knows about engines was not at the garage today but the bike past mot.

I will take the head off and have a look and see whats going on.
Offline Profile Quote Post Goto Top
 
bolder Aug 12 2016, 06:35 PM Post #7
The 65mph Club Member
[ *  *  *  *  * ]
Posts:
149
Group:
Members
Member
#6,413
Joined:
May 13, 2012
Jasper Carrots Funky Moped
Aug 12 2016, 05:37 AM
bolder
Aug 10 2016, 09:38 PM
Hi,

I have two bikes both 394 type. fitted with par ma kits and cut disco.

The one is running fine has 170 main jet. needle valve one notch down from middle and air screw out 2.5 turns out.
The bike starts easy and goes well.

The problem bike has a 170 main jet.

When the air screw is 2.5 turns out the bike is a pig to start,so I reset it at its highest revs on tick over which was 2 turns out and then reset it for best throttle response which is 1.5 turns out .
The bike starts alot better .
When the needle valve is set in the middle groove the bike goes well but the engine makes alot of noise like piston slap, pinking sound or metal to metal sound not good.
When the needle valve is set in the one groove down from mid. (richer) the bike smokes and bogs down mid. range but the engine sounds alot better.
Then I adjusted the mixture screw to 2 then 2.5 turns out to make it weaker still bogs down and don't like starting.

Tried a 165 jet in carb. and done all of the above but the engine was very noisy.

I've change plug from a 7 to a 9 no change.

Both bikes run on supper unleaded.

What would you say to look at next timing.

Thank for looking


Your problem engine sounds exactly the same as mine, or should I say did, as at this very moment it is off the bike and in a garage hopefully getting unseized :X
Hope you get it sorted mate .
Hopefully I won't have to cross that bridge .
Good luck
Offline Profile Quote Post Goto Top
 
yellow dx Sep 8 2016, 06:51 PM Post #8
Two Fizzy's in the village
[ *  *  *  *  * ]
Posts:
315
Group:
Members
Member
#6,719
Joined:
April 6, 2013
Bolder,

have you tried swopping the head, piston, and barrel between the two bikes? It isn't too much work and should reveal something conclusive!

what's the latest?

cheers
Offline Profile Quote Post Goto Top
 
mech73 Sep 9 2016, 07:51 AM Post #9
Member Avatar
Fizzmeister Extrodinaire
[ *  *  *  *  *  * ]
Posts:
3,067
Group:
Members
Member
#2,607
Joined:
May 19, 2007
bolder
Aug 12 2016, 06:30 PM
Hi Mark,

I am only using 33-1 because that was on the instruction with the parma kits,Also set the timing to 1.4 BTDC ?

so if it is piston slap running it on 33-1 could be the cause?

When I use 20-1 mix will I have to change the carb setting?

Took the bike for mot and it started first time bog down for first mile then was ok.

The guy that knows about engines was not at the garage today but the bike past mot.

I will take the head off and have a look and see whats going on.
Sorry must have missed these questions when I was away.

I don't think 33:1 will be the cause of the piston slap, not in the short term anyway. I'd personally put more oil in, but I don't think it's the cause of your issue. The advised timing change suggests the compression ration has been increased. A higher compression ratio in itself will increase heat and does make an engine more sensitive. I certainly wouldn't advance the ignition back to the standard 1.8 or pre-ignition or detonation could result.

I think this weak oil mix idea mainly comes from racing. A lot of motocrossers use very weak fuel/oil mixes, but they're often water cooled and are constantly on and off the throttle, either accelerating flat out or braking. Road racers tend to use a bit more oil, but on most tracks they're still not held flat out for more than a few 10s of seconds. In both cases during the 'off throttle' sections oil builds up in the crank case and is used on the next flat out section. Fizzies on the other hand can be held flat out in top for many minutes or longer and they have a fairly small fin area so get very hot. In certain types of use, they don't have much 'off throttle' time, and have to rely totally on the oil that condenses out whilst flat out.

In theory increasing the amount of oil in the fuel will weaken the mixture, but the effect is very small. I've found that the bike tends to be a bit more sensitive to an over rich mixture when there's more oil in the fuel. ie it is more likely to four stroke (splutter) especially when cold, I think this is when it's burning off any excess oil that's built up in the crankcase. It should clear in the first mile or so.

Bogging is usually due to an over weak mixture especially at part throttle. That's more of a losing power or cutting out like it's running out of fuel. Most bikes will do that to some extent if you try to ride off without choke too quickly after start up especially in cold weather.

Offline Profile Quote Post Goto Top
 
1 user reading this topic (1 Guest and 0 Anonymous)
« Previous Topic · Fizzy Problem Solving · Next Topic »
Add Reply

Track Topic · E-mail Topic Time: 8:58 AM Jul 11
Hosted for free by ZetaBoards · Privacy Policy