colder temps affect carbs?

TeddyG

TeddyG

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Location
Portland Oregon
My 750 SF2 was running like a top during warm weather w instant start up and no plug fouling. Now that temps are dropping, it,s been fouling the B8 plugs at start up and idling lower. Switching to hotter B7 plugs, it,s now starting better w cleaner plugs. Just wondering if others have experienced this, thanks.
 
How long are you keeping the Choke on? Best to get the Choke off ASAP. The choke can allow fouling if kept on; it doesn't take long. They sell triple-tapered needle kits for modern Kehans developed on Dinos that include charts that show changes for Temperature and Altitude. Great for absolute performance, but Dels on Laverdas shouldn't require the need to be jetted to within that tight a range. Just my 2c, but it should require choke to start, then just about immediately turn the choke off and be able to ride away easily, baby it for a few minutes to warm up and Bob's your uncle. If it's not, then jetting might need a fiddle. I don't like going down the hotter plug route. People melt pistons, and that's such a catastrophe. Add in posable weak springs in the timing advance and? Plenty here know way more than me, should be an interesting thread.
 
My SF2 here in the sub arctic gets ridden in under 10degC early and late riding season and over 30 in the summer, it does not need any tuning changes and has never fouled a plug. It has ancient Champion N3 that have been in it forever, even refitted after engine work. With B7 in your bike you have a good chance to foul a plug with melted piston. High altitude can have an effect but generally the loss of power is more significant, I rode over the alps on it last summer and never had a problem. There has been enough written on this forum regarding plug ranges for twins. Your choice.
 
Something very amiss there, Teddy. Like Tippie, I run my hot hi-comp 880 on B9s, summer and winter (close to 0C) on a cold winter morning. B7s is just wrong. Almost sounds like you're getting a weak spark.

When I had Dells and a stock moto I probably covered 250,000km summer and winter on B9s and never - not even once - fouled a plug. Seen too many SFs with lovely small-end inspection holes in the piston crowns for me to ever try hotter plugs.
 
Holing pistons is not a way to cure carb problems. 7s are way too hot.
Cold air is denser and contains more oxygen but won't affect carburation much. You can however feel it when riding.
You need to go through all the engine tune to determine if your problem is carb related.
An SF2 is very forgiving re carb tune in normal street use.
You have something very wrong.
Paul
 
OK, that answers my question. I,m wary of holing the pistons and will go back to 8s and look over the cable routing and try rejetting. I use the enricher only briefly during start up. the colder temps might be affecting the battery so I,ll keep it charged on a tender.
 
If the battery has enough juice to turn the .95hp starter motor I wouldn't be too concerned about the battery. Make sure your wiring connections to your coils are good. I've seen considerable voltage drops in this area on SFs with old wiring.
 
piranha-bro2 said:
If the battery has enough juice to turn the .95hp starter motor I wouldn't be too concerned about the battery. Make sure your wiring connections to your coils are good. I've seen considerable voltage drops in this area on SFs with old wiring.
Click to expand...
I put a 350 cca AGM battery in my triple and the engine turned over much faster on starting making the enrichers richer and I had to get off them much sooner as Vince noted.
 
Probably opening a can of worms here, but here goes. The correct way to apply the choke to a cold engine start-up is.
In Neutral, of course
Turn the fuel taps on
Don't touch the choke lever yet.
Turn the ignition on
Then, simultaneously as you hit the starter button, slowly pull on the choke lever; the instant the engine fires up, that is the setting you need. Do not keep pulling on the choke lever, as you will risk fouling the plugs.
That's it, it's simple. Too many owners pull on the choke lever before hitting the starter button, often applying a full choke when not necessary. HTH
 
Thanks JotaDave- I'll try that.
I've been first engaging the enricher lever, turning on the ignition, and immediately lowering the enricher back in place to keep the revs down, and then holding the throttle slightly open to maintain a steady idle @ 1K RPM until it warms up. This has worked fine in warmer temps w B8 plugs, but I've noticed the left side plug is always burning richer than the right side. Both carbs have been totally rebuilt w the same jetting and the bike always started instantly with no problems until the colder weather. The enricher and throttle cables are all routed correctly and not hanging up and I'll re-check the synching. The battery is fully charged and since it starts immediately, I'm assuming that the coils are fine.
So I'm guessing the left side carb has to be re-jetted to compensate for burning slightly richer than the right carb.
 
TeddyG said:
So I'm guessing the left side carb has to be re-jetted to compensate for burning slightly richer than the right carb.
Click to expand...
Doesn't add up in a motor with identical L and R systems. My point about spark quality would fit with a spark good enough to get a motor going but falter (and foul a plug) when extra fuel load is added to the equation. Same reason a motor will miss at high loads when it doesn't at lower loads. Is there a way to check the strength of the spark on both sides? Maybe someone with more elektrickery expertise can answer that.
 
You can buy gadgets like a spark plug, but they have a movable gap; you can jack the gap out to quite big dimensions. Compare each side to see if they're the same
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