JunkVlog: Supermoto questions, Carb problems and more!

1/25/2016

Supermoto questions, Carb Problems, and more! Leave your questions in the comments below or in the video!

George

8/26/2016 09:30:57 am

cleaned carb on 110 pit bike lifan block started first time now wont start again fuel and spark both there any advice would be most welcome

The Junk Man ADV link

8/26/2016 05:06:40 pm

Not a whole lot to go on, but sounds like you are not getting enough fuel, meaning it is something with the jetting.

Matt

10/14/2016 02:26:19 pm

Hi,
I was hoping for an insight into my 1974 F7 issues.
I received the bike in complete pieces and built the motor up from the crank.
I have replaced all seals and gaskets including new crank seals during the rebuild. Also fitted was a new piston along with a cylinder honing.

The bike will not start...it feels like it wants to but there is definately something off.

The carburteor has been gone through several times with the float height being adjusted correctly and all seals, gaskets replaced.

I have succesfully tested the cases for leak down.
I have a great spark and the timing marks are all lined up, I have tried tweaking the plate to check if this helps..it does not.

I have tested the rotary valve timing and the valve appears to open at 115 degree BTDC and closes at 55 degrees ATDC, (specs for year I believe)

I have the valve timed up with the mark aligned to the crankshaft dowel.
Is it possible that the mark should be aliged with the woodruff key?
I do not seem to be getting a good amount of vacuum through the intake when the bike is kicked over.
The raotay valve and cover are in spec.

Any help would be most appreciated as I have torn into this many times without success so far.

Many thanks.

The Junk Man ADV link

10/15/2016 07:32:29 am

Sounds like you have everything correct and it should run. This tells me something very small is the cause, but what I don't know. Run through your fuel, spark, and compression again.

matt

10/15/2016 04:39:46 pm

I have rechecked the igntion timing a few times and validated the spark...(very nice blue spark).
The carb has been gone through a few times, however the plug is definately gettimng fuel...perhaps too much, although I have re-checked the carb and float height etc many times also....I can conduct another compression test however on the kickstart it feels like very good compression.

I'm at a loss to be honest

The Junk Man ADV link

10/15/2016 05:33:53 pm

Did you pressure test the crankcase?

Victor

10/7/2017 04:56:13 pm

I have a 2002 Honda Shadow Spirit vt750dc and I need to adjust the rpm. I bought ez-tach 380 and I need to input the number of strokes per cycles. I know that it's a 4
stroke but I don't know per cycles.I could input 4:1, 4:2, 4:4. Please advise. Thank you.

Jon Rhodig link

10/8/2017 12:10:32 pm

What do the directions say? 4 stroke is the same as 4 cycle. If I had to guess 4:2 since the Shadow is a twin.

Chris Darwin

2/26/2018 05:12:49 pm

I have a 75' 350 Bighorn with 1066 miles, bought from original owner. Mint condition!! I just wanted it for bombing around our village, not racing. I'm a bigger guy and this bike fits me great!! Plus, it really gets second looks and comments. I love this thing!! So....what's the ???
Went through all seals(Klemmvintage ) carb parts ultrasonic dipped.
Starts 2nd kick consistently, hauls ass in general!! It seems this bike likes to be on the pipe,all the time! It has a surging on decel and seems hard to hold at a "steady" throttle when at say; 20-35 mph.??
Again, it starts ,idles, and just plain gets it!! But maybe being a two-stroke, it's just the nature of the beast?? You sure seem to have spent your fair share of time on these Bighorns, John. I flat think they're a cool bike! But, any insight is very appreciated here in the Great white North! Thanks for your time!!👍🏻

James E Kuss link

7/20/2018 10:57:39 pm

If 130 BTDC = 130 degrees Before Top Dead Center,
and if 60 ATDC = 60 degrees After Top Dead Center,
Then the valve you show could not be a modified one!
After all 130 + 60 = 190 degrees and that is more than half the disc.

j.kuss

Scott

8/21/2018 05:19:38 am

Recently purchase two F7s and have found your videos to be very helpful. I clicked on the video regarding sourcing parts but wonder if you could provide more info with regards to this subject. My 72 needs various odds and ends but I'm finding it difficult to locate what I thought would be readily available.

THEJUNKMAN link

8/21/2018 06:09:02 am

What kind of info do you want? Start with OEM parts suppliers for your things like seals, gaskets and some bearings and the likes. You will be surprised to find what is still available since those parts can be common across many models and years. Otherwise Ebay and the general internet is going to be the only way to find body or cosmetic parts. You can visit or call some junkyards, but those will be hit or miss. You will just have to be patient and keep checking various places for the parts you need. They turn up all the time.

Scott

8/21/2018 07:38:09 am

Thanks for the reply. I seem to be having trouble finding gasket sets. I will need a piston. Rings then cosmetics. I've followed the big horn videos and have removed the engine. Mine wasn't seized and when manual arrives I'll check specs but right it looks like everything will be fine. The engine had been blowing oil past the rings as the muffler was full of oil and the case itself was covered.

THE JUNK MAN ADV link

8/21/2018 09:44:45 am

The F7 is a 2 stroke, so blowing oil out of the exhaust is completely normal. The rings are only for compression as there is no crankcase oil. The F7 is a rotary valve so the fue/air & oil mix enter into the crankcase and move into the top of the cylinder via transfer ports. The expelled gases and burnt/unburnt oil exit the exhaust. It is possible the gasket for the exhaust flange is leaking a bit as well as is the crush gasket where the exhaust fits into the flange.

A good amount of gaskets are still available OEM, but for those that aren't there are tons of various gaskets as NOS and aftermarket all over Ebay. Pistons and rings will be exclusively an Ebay proposition as will the cosmetics.

On a side note. Be watching my Youtube channel, I live stream where I take live questions as well as I have some videos coming that address some of your challenges.

Scott

8/21/2018 10:14:25 am

Thanks, I understand there isn't any crankcase oil but it seems as there is quite a bit of oil in the crankcase and the muffler had oil in it to the point that I poured some out. The cylinder is black. It also had an oddball spark plug that someone used. The oil tank was half full. Maybe someone pumped oil into it trying to start it. Is that possible? I think the parts bike F9 I think can also be brought back to life. Look forward to the live video.

Noah link

1/11/2021 10:34:31 am

Thank you for writing tthis

JunkVlog: Supermoto questions, Carb problems and more!

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