Logbooks of '72 R75/5, '79 R100T, '82 R80G/S Paris-Dakar, '93 R100GS PD, '71 CB750 and others, a.k.a.
Jetting a dual-plugged 1000cc CR9.7 engine
So, here I am with my bitsa engine that has the following specs:
- 11/1980 R100CS bottom end
- 11/1980 R100CS big valve (40/44) heads, shaved for planarity, reworked and dual-plugged (lower plugs are 10mm with 1/2in reach)
- 06/1978 R100S barrels (iron lined) and pistons ("A", dome no squish), estimated CR9.7
- spark plugs: NGK BPR6ES (top) and NGK D6HA (bottom)
- 40mm Bings jetted for 81-'83 R100CS/RS/RT (94/40/113 & 114: 160/2.66/45/2nd)
- stock R100R 2-into-1 exhaust
The first 12,000km were done in 4 weeks on two big trips and the plugs looked like this:
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| LH plugs, bottom plug slightly wet (oil fouled?), no gas smells |
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| RH plugs, RH carb needle was set wrong at 3rd, both plugs smell of gas as a result, lower plug seems oil foiled (?) |
The left top plug has the best appearance: heat range is correct, good tan look on the isolator, no considerable break away of porcelan, but the lower plugs are a lot darker. They seem oil fouled but oil consumption of the engine is at about 0.2l/1000km. However, when I remove the valve covers for valve adjustments I think there is a lot more oil in the covers then there was in the R80G/S or R100T I owned.
I guess I have to have a look into re-jetting and first put the information together for the different carb setting of the high compression engines:
| Main Jet | Needle Jet | Idle Jet | Needle position | Bing P/N | Comment |
| '77 R100S | 170 | 2.66 | 45 | 3rd
| 94/40/103 & 104 | Clymer data |
'77 R100RS | 170 | 2.68 | 45 | 2nd
| 94/40/105 & 106 | Clymer data
| '78 R100S/RS | 160 | 2.64 | 45 | 2nd
| 94/40/107 & 108 | Clymer data
| '79 R100T | 170 | 2.66 | 45 | 3rd | 94/40/103 & 104 | Clymer data
| '79 R100S/RS/RT | 170 | 2.68 | 45 | 2nd
| 94/40/105 & 106 | Clymer data'80 R100S/T/RS/RT | 160 | 2.66 | 45 | 2nd
| 94/40/109 & 110 | Clymer data 81-'83 R100CS/RS/RT | 160 | 2.66 | 45 | 2nd
| 94/40/113 & 114 | Clymer data
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These setting obviously don't take dual plugging into consideration and I am disputing if there was a necessity to re-jet, if it wasn't for the R100R exhaust that normally works in a 1000cc engine with a CR of 8.2. I think the engine runs rich and the grey tan of the top plug is fooling me when I look at the lower plugs.