Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

Francis Davis /

Jun 30, 2019 06:25PM

Hey,

Thanks in advance for your help! Bikes running pretty well overall, had it out for a 30-mile ride this morning. Sunny day in Cleveland! Bike seems to be running a bit hot (to my knowledge) head temp gauge attached on top of spark plug is reading between 365-400 at WOT on flat ground. I've got the Airsal high performance 50cc kit, 15:15 SHA with derestricted intake manifold and a 70 jet. No other engine work. Stock exhaust. Running about 32mph flat out. There seems to be a bit of "four-stroking" (again, to my ears) at top speed. I'm wondering at this point if the exhaust is the limiting factor in the system, but I'm not sure. You might have a better idea than I. I have a recording of the engine sound at top speed attached.

Re: Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

A Fouler Fowler /

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fowler

Jun 30, 2019 06:28PM

Four-stroking and hot don't go together. Mush have an airleak or maybe ignition timing. I had a 40t with a similar setup that would get up to 40mph.

I hear four-stroking up top. Sounds pretty good otherwise. Though it could also be your points floating due to high rpms. Or maybe Points arching? (edited)

Re: Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

Rebel Moby /

rebelmoby

Jul 01, 2019 09:47AM

Check our ignition timing, you need to be around 1,2-1,5mm BTDC, the less advance will also aid in cooling as well as giving a more robust power band..

The pea-shooter exit pipe on the exhause will be holding you back. I suggest trying to replace the exit pipe with one that is 11-12mm inside diameter and half the length of the stock original. I find it is easier to just fabricate a new end plate than to mess with the original. If you find the new setup is too loud for you (or neighbours) you can cap the inside end of the new exit pipe and drill some #30 (1/8 inch) holes in the pipe to make a piccolo baffle out of it that will diffuse some of the sound.

You will need to adjust your jetting for the better breathing pipe.

Read your plug for other helps than just jetting

Re: Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

Daniel '' /

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deesal

Jul 02, 2019 02:53PM

We missed you rebel Moby

Re: Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

Graham Motzing /

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grahammotzing

Jul 02, 2019 04:27PM

yeah that plug graphic is a trip, i've never seen that before.. you reckon its accurate?

i got a bike that is giving me some hassle right now, the steel base of the threads where it says 'jetting read flat... blah blah' is super black... electrode looks pretty ok. i was thinking it might be a leaking trans side seal, but maybe i'm just super rich? shouldn't be.

i'm also starting to think it has a weak spark or something to that nature. dirty points, etc. might swap stators before going all gung ho.

Re: Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

Rebel Moby /

rebelmoby

Jul 02, 2019 09:16PM

Thanks

> Daniel '' Wrote:

> -------------------------------------------------------

> We missed you rebel Moby

Re: Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

Rebel Moby /

rebelmoby

Jul 02, 2019 09:20PM

That is how I have been reading plugs and it has never let me down.

Might be dirty points or resistor in the cap is starting to die slowly...

> Graham Motzing Wrote:

> -------------------------------------------------------

> yeah that plug graphic is a trip, i've never seen that before.. you

> reckon its accurate?

>

> i got a bike that is giving me some hassle right now, the steel base of

> the threads where it says 'jetting read flat... blah blah' is super

> black... electrode looks pretty ok. i was thinking it might be a

> leaking trans side seal, but maybe i'm just super rich? shouldn't be.

>

> i'm also starting to think it has a weak spark or something to that

> nature. dirty points, etc. might swap stators before going all gung ho.

Re: Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

Graham Motzing /

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grahammotzing

Jul 03, 2019 12:27AM

Hmm good thought on the plug cap, it's an og Puch that I've kept around because it's got really nice chrome but might be failing

Re: Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

P D /

pdcomm

Jul 03, 2019 11:00AM

> Graham Motzing Wrote:

> -------------------------------------------------------

> yeah that plug graphic is a trip, i've never seen that before.. you

> reckon its accurate?

Big Honda guys been using that 'guide' for years with excellent results .

Re: Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

Graham Motzing /

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grahammotzing

Jul 03, 2019 12:42PM

yeah the problem with plug chops and all this plug tuning stuff is that its assuming the only variable you changed is the one in question. also tough to tell if they are talking 4T or 2T or if it even matters.

there is a thread on '2 stroke r+d' facebook group about carbon deposits on the piston face, everyone talking like 'too rich, too lean' or 'too much timing, not enough timing' etc, but that is assuming everything is tuned perfecto and you just went up/down on jetting or up/down on timing.

in the real world tuning never works that good, especially when you have an engine that isn't running happy and you are using stuff like plug chopping to try to figure out why.

over the years i've seen dozens (hundreds) of people seize bikes with dark plugs becase they had ignition problems and kept going leaner to chase that brown plug. I have had a few perfectly tuned bkes that left the plug very very light brown, you'd think they were lean but they were just dialed right in. Heat range also fucks with plug reading so who knows.

Re: Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

Rebel Moby /

rebelmoby

Jul 04, 2019 06:14PM

Indeed - seen enough folks seize a 'four stroking' motor by leaning it out when it was misfiring due to a ignition fault.

> Graham Motzing Wrote:

> -------------------------------------------------------

> yeah the problem with plug chops and all this plug tuning stuff is that

> its assuming the only variable you changed is the one in question. also

> tough to tell if they are talking 4T or 2T or if it even matters.

>

> there is a thread on '2 stroke r+d' facebook group about carbon deposits

> on the piston face, everyone talking like 'too rich, too lean' or 'too

> much timing, not enough timing' etc, but that is assuming everything is

> tuned perfecto and you just went up/down on jetting or up/down on

> timing.

>

> in the real world tuning never works that good, especially when you have

> an engine that isn't running happy and you are using stuff like plug

> chopping to try to figure out why.

>

> over the years i've seen dozens (hundreds) of people seize bikes with

> dark plugs becase they had ignition problems and kept going leaner to

> chase that brown plug. I have had a few perfectly tuned bkes that left

> the plug very very light brown, you'd think they were lean but they were

> just dialed right in. Heat range also fucks with plug reading so who

> knows.

Re: Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

kevin smellaflange /

kevinsmells

Jul 05, 2019 08:10PM

thanks for swinging back, rebel Moby

Re: Stockish Motobecane A Bit Hot and Four Strokey" AT WOT

Rebel Moby /

rebelmoby

Jul 06, 2019 07:41AM

Thanks - I think - now folks will think I swing both ways...

> kevin smellaflange Wrote:

> -------------------------------------------------------

> thanks for swinging back, rebel Moby

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